feat(nodejs): expose connectNamespace for namespace-backed connections (#3383)

### Summary 

Adds a `connectNamespace(implName, properties, options?)` to the NodeJS
SDK`. Closes #3380.

### Testing
- pnpm test
- Ran smoke test

```
import { connectNamespace } from "lancedb"
import { tmpdir } from "os";
import { mkdtempSync } from "fs";
import { join } from "path";

const dir = mkdtempSync(join(tmpdir(), "lancedb-connect-namespace-smoke-"));
console.log(`Using temp dir: ${dir}\n`);

// 1. Happy path: connect via the "dir" namespace impl, create + list a table.
console.log('Connecting via connectNamespace("dir", { root })...');
const db = await connectNamespace("dir", { root: dir });
console.log("  ✓ connected:", db.display());

console.log("Creating a table and listing it...");
await db.createTable("users", [
  { id: 1, name: "alice" },
  { id: 2, name: "bob" },
]);
console.log("  ✓ tableNames ->", await db.tableNames());

const table = await db.openTable("users");
console.log("  ✓ users.countRows ->", await table.countRows());

// 2. Storage options pass-through.
console.log("\nReconnecting with storageOptions (plumbing check)...");
const dbWithOpts = await connectNamespace(
  "dir",
  { root: dir },
  { storageOptions: { newTableDataStorageVersion: "stable" } },
);
console.log("  ✓ connected with storageOptions:", dbWithOpts.display());
await dbWithOpts.close();

// 3. Empty implName -> clear error.
console.log("\nCalling connectNamespace('', {}) (expect error)...");
try {
  await connectNamespace("", {});
  console.error("  UNEXPECTED: empty implName did not throw");
} catch (err) {
  console.log(`  ✓ Got expected error: ${err.message.split("\n")[0]}`);
}

// 4. Unknown impl -> error.
console.log("\nCalling connectNamespace('not-a-real-impl', {}) (expect error)...");
try {
  await connectNamespace("not-a-real-impl", {});
  console.error("  UNEXPECTED: unknown impl did not throw");
} catch (err) {
  console.log(`  ✓ Got expected error: ${err.message.split("\n")[0]}`);
}

// 5. Create a table inside a child namespace, then reconnect with a fresh
//    connectNamespace call and confirm the table is reachable via that
//    namespace path. (The dir+manifest impl keeps the namespace hierarchy in
//    a root manifest, so "scoping" happens via namespacePath args, not by
//    pointing root at a subdir.)
console.log("\nCreating a table inside a child namespace...");
const dir2 = mkdtempSync(join(tmpdir(), "lancedb-connect-namespace-smoke-"));
const writer = await connectNamespace("dir", {
  root: dir2,
  manifest_enabled: "true",
});
await writer.createNamespace(["analytics"]);
await writer.createTable(
  "orders",
  [
    { id: 1, total: 10 },
    { id: 2, total: 20 },
  ],
  ["analytics"],
);
console.log(
  "  ✓ writer sees tables under [analytics] ->",
  await writer.tableNames(["analytics"]),
);
await writer.close();

console.log("Reconnecting and reading the table via its namespace path...");
const reader = await connectNamespace("dir", {
  root: dir2,
  manifest_enabled: "true",
});
console.log(
  "  ✓ reader tableNames(['analytics']) ->",
  await reader.tableNames(["analytics"]),
);
const orders = await reader.openTable("orders", ["analytics"]);
console.log("  ✓ orders.countRows via reader ->", await orders.countRows());
await reader.close();

await db.close();
console.log("\nAll checks passed.");
```

```
Using temp dir: /var/folders/bj/hn6jv9c50y301d1nx0y8xmn00000gn/T/lancedb-connect-namespace-smoke-WByF1P

Connecting via connectNamespace("dir", { root })...
  ✓ connected: LanceNamespaceDatabase
Creating a table and listing it...
  ✓ tableNames -> [ 'users' ]
  ✓ users.countRows -> 2

Reconnecting with storageOptions (plumbing check)...
  ✓ connected with storageOptions: LanceNamespaceDatabase

Calling connectNamespace('', {}) (expect error)...
  ✓ Got expected error: implName must be a non-empty string

Calling connectNamespace('not-a-real-impl', {}) (expect error)...
  ✓ Got expected error: Invalid input, Failed to connect to namespace: Namespace { source: Unsupported { message: "Implementation 'not-a-real-impl' is not available. Supported: dir, rest" }, location: Location { file: "/Users/brendan/.cargo/git/checkouts/lance-8ddea23c38163eda/f693245/rust/lance-namespace-impls/src/connect.rs", line: 216, column: 14 } }

Creating a table inside a child namespace...
  ✓ writer sees tables under [analytics] -> [ 'orders' ]
Reconnecting and reading the table via its namespace path...
  ✓ reader tableNames(['analytics']) -> [ 'orders' ]
  ✓ orders.countRows via reader -> 2

All checks passed.
```

### Docs
- regenerated docs

nodejs/lancedb/index.ts

@@ -8,6 +8,7 @@ import {
 } from "./connection";
 
 import {
+  ConnectNamespaceOptions,
   ConnectionOptions,
   Connection as LanceDbConnection,
   JsHeaderProvider as NativeJsHeaderProvider,
@@ -22,6 +23,7 @@ export { JsHeaderProvider as NativeJsHeaderProvider } from "./native.js";
 export {
   AddColumnsSql,
   ConnectionOptions,
+  ConnectNamespaceOptions,
   IndexStatistics,
   IndexConfig,
   ClientConfig,
@@ -300,3 +302,197 @@ export async function connect(
   );
   return new LocalConnection(nativeConn);
 }
+
+/**
+ * Configuration for the built-in directory namespace (`"dir"`).
+ *
+ * The directory namespace stores tables under a single root path (local
+ * filesystem or object storage URI). See
+ * {@link https://docs.lancedb.com/namespaces} for the documented surface;
+ * less-common knobs live under {@link DirNamespaceConfig.extraProperties}.
+ */
+export interface DirNamespaceConfig {
+  /** Root path or URI containing the LanceDB tables. */
+  root: string;
+  /**
+   * Whether to maintain a namespace manifest at the root. Required for
+   * child namespaces. Defaults to true on the impl side.
+   */
+  manifestEnabled?: boolean;
+  /**
+   * Additional raw properties passed verbatim to the namespace
+   * implementation (e.g. `storage.*`, `credential_vendor.*`). Typed
+   * fields above take precedence on key collision.
+   */
+  extraProperties?: Record<string, string>;
+}
+
+/**
+ * Configuration for the built-in REST namespace (`"rest"`).
+ *
+ * The REST namespace talks to a remote catalog server over HTTP. See
+ * {@link https://docs.lancedb.com/namespaces} for the documented surface;
+ * less-common knobs (TLS, metrics) live under
+ * {@link RestNamespaceConfig.extraProperties}.
+ */
+export interface RestNamespaceConfig {
+  /** Catalog endpoint URL. */
+  uri: string;
+  /**
+   * HTTP headers forwarded with each request. Keys are passed through
+   * as-is (e.g. `"x-api-key"`, `"Authorization"`).
+   */
+  headers?: Record<string, string>;
+  /**
+   * Additional raw properties passed verbatim to the namespace
+   * implementation (e.g. `tls.*`, `ops_metrics_enabled`, `delimiter`).
+   * Typed fields above take precedence on key collision.
+   */
+  extraProperties?: Record<string, string>;
+}
+
+function dirConfigToProperties(
+  config: DirNamespaceConfig,
+): Record<string, string> {
+  // Spread the whole input so that unknown keys (e.g. a raw `manifest_enabled`
+  // passed via the dynamic-impl path) flow through instead of being dropped.
+  // Typed transformations layer on top.
+  const { manifestEnabled, extraProperties, ...rest } = config;
+  const properties: Record<string, string> = {
+    ...(extraProperties ?? {}),
+    ...(rest as Record<string, string>),
+  };
+  if (manifestEnabled !== undefined) {
+    properties.manifest_enabled = String(manifestEnabled);
+  }
+  return properties;
+}
+
+function restConfigToProperties(
+  config: RestNamespaceConfig,
+): Record<string, string> {
+  const { headers, extraProperties, ...rest } = config;
+  const properties: Record<string, string> = {
+    ...(extraProperties ?? {}),
+    ...(rest as Record<string, string>),
+  };
+  if (headers) {
+    for (const [name, value] of Object.entries(headers)) {
+      properties[`headers.${name}`] = value;
+    }
+  }
+  return properties;
+}
+
+/**
+ * Connect to a LanceDB database through a namespace.
+ *
+ * Unlike {@link connect}, which routes by URI scheme (local path vs.
+ * `db://` cloud), `connectNamespace` always returns a namespace-backed
+ * connection. The `implName` selects the namespace implementation:
+ *
+ * - `"dir"` — directory namespace, configured with {@link DirNamespaceConfig}.
+ * - `"rest"` — remote REST catalog, configured with {@link RestNamespaceConfig}.
+ * - Any other string — full module path for a custom implementation,
+ *   configured with a free-form string-keyed `properties` map.
+ *
+ * @example Typed dir namespace
+ * ```ts
+ * const db = await connectNamespace("dir", { root: "/path/to/db" });
+ * await db.createTable("users", [{ id: 1 }]);
+ * ```
+ *
+ * @example Typed REST namespace with auth headers
+ * ```ts
+ * const db = await connectNamespace("rest", {
+ *   uri: "https://catalog.example.com",
+ *   headers: { "x-api-key": process.env.CATALOG_KEY ?? "" },
+ * });
+ * ```
+ *
+ * @example Custom implementation with raw properties
+ * ```ts
+ * const db = await connectNamespace("my.custom.Namespace", {
+ *   endpoint: "...",
+ * });
+ * ```
+ */
+export function connectNamespace(
+  implName: "dir",
+  config: DirNamespaceConfig,
+  options?: Partial<ConnectNamespaceOptions>,
+): Promise<Connection>;
+/**
+ * Connect through the built-in REST namespace.
+ *
+ * Configured with {@link RestNamespaceConfig}. See the function-level
+ * documentation above for the full surface, examples, and how this
+ * relates to {@link connect}.
+ *
+ * @example
+ * ```ts
+ * const db = await connectNamespace("rest", {
+ *   uri: "https://catalog.example.com",
+ *   headers: { "x-api-key": process.env.CATALOG_KEY ?? "" },
+ * });
+ * ```
+ */
+export function connectNamespace(
+  implName: "rest",
+  config: RestNamespaceConfig,
+  options?: Partial<ConnectNamespaceOptions>,
+): Promise<Connection>;
+/**
+ * Connect through a custom namespace implementation by full module path,
+ * configured with a free-form string-keyed `properties` map. Use the
+ * typed overloads above for the built-in `"dir"` and `"rest"` impls.
+ *
+ * See the function-level documentation above for examples and how this
+ * relates to {@link connect}.
+ *
+ * @example
+ * ```ts
+ * const db = await connectNamespace("my.custom.Namespace", {
+ *   endpoint: "...",
+ * });
+ * ```
+ */
+export function connectNamespace(
+  implName: string,
+  properties: Record<string, string>,
+  options?: Partial<ConnectNamespaceOptions>,
+): Promise<Connection>;
+export async function connectNamespace(
+  implName: string,
+  configOrProperties:
+    | DirNamespaceConfig
+    | RestNamespaceConfig
+    | Record<string, string>,
+  options?: Partial<ConnectNamespaceOptions>,
+): Promise<Connection> {
+  let properties: Record<string, string>;
+  if (implName === "dir") {
+    properties = dirConfigToProperties(
+      configOrProperties as DirNamespaceConfig,
+    );
+  } else if (implName === "rest") {
+    properties = restConfigToProperties(
+      configOrProperties as RestNamespaceConfig,
+    );
+  } else {
+    properties = configOrProperties as Record<string, string>;
+  }
+
+  const finalOptions: ConnectNamespaceOptions = (options ??
+    {}) as ConnectNamespaceOptions;
+  finalOptions.storageOptions = cleanseStorageOptions(
+    finalOptions.storageOptions,
+  );
+
+  const nativeConn = await LanceDbConnection.newWithNamespace(
+    implName,
+    properties,
+    finalOptions,
+  );
+  return new LocalConnection(nativeConn);
+}