feat(nodejs): add namespace management methods on Connection (#3371)

### Summary

Closes #3363 

Adds the four namespace management methods to the NodeJS `Connection`,
bringing parity with the Rust core and Python bindings:

- `listNamespaces(parent?, options?)`
- `createNamespace(namespacePath, options?)`
- `dropNamespace(namespacePath, options?)`
- `describeNamespace(namespacePath)`

### Test plan
- npm test
- Ran a smoke test script

```typescript
import { connect } from '<lancePath>'
import { tmpdir } from "os";
import { mkdtempSync } from "fs";
import { join } from "path";

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

const db = await connect(dir, {
  namespaceClientProperties: { manifest_enabled: "true" },
});

console.log("Creating namespaces...");
await db.createNamespace(["analytics"]);
await db.createNamespace(["analytics", "sales"], {
  properties: { owner: "brendan", purpose: "smoke-test" },
});
await db.createNamespace(["marketing"]);

const root = await db.listNamespaces();
console.log("Root namespaces:", root.namespaces);

const children = await db.listNamespaces(["analytics"]);
console.log("Children of 'analytics':", children.namespaces);

const descWithProps = await db.describeNamespace(["analytics", "sales"]);
console.log("Describe analytics/sales (with properties):", descWithProps);

const descNoProps = await db.describeNamespace(["analytics"]);
console.log("Describe analytics (no properties):", descNoProps);

console.log("Describing a non-existent namespace (expect error)...");
try {
  await db.describeNamespace(["does-not-exist"]);
  console.error("  UNEXPECTED: describe succeeded for non-existent namespace");
} catch (err) {
  console.log(`  ✓ Got expected error: ${err.message.split("\n")[0]}`);
}

await db.dropNamespace(["marketing"]);
const afterDrop = await db.listNamespaces();
console.log("Root after dropping marketing:", afterDrop.namespaces);

await db.close();
console.log("\nAll operations completed successfully.");
```

```
Using temp dir: /var/folders/bj/hn6jv9c50y301d1nx0y8xmn00000gn/T/lancedb-smoke-MUC5NI

Creating namespaces...
Root namespaces: [ 'analytics', 'marketing' ]
Children of 'analytics': [ 'sales' ]
Describe analytics/sales (with properties): { properties: { purpose: 'smoke-test', owner: 'brendan' } }
Describe analytics (no properties): {}
Describing a non-existent namespace (expect error)...
  ✓ Got expected error: lance error: Namespace error: Namespace not found: does-not-exist, rust/lance-namespace-impls/src/dir/manifest.rs:2495:14  Caused by: Namespace error: Namespace not found: does-not-exist, rust/lance-namespace-impls/src/dir/manifest.rs:2495:14    Caused by: Namespace not found: does-not-exist
Root after dropping marketing: [ 'analytics' ]

All operations completed successfully.
```

### Documentation
- regenerated docs

docs/src/js/classes/Connection.md

@@ -148,6 +148,33 @@ Creates a new empty Table
 
 ***
 
+### createNamespace()
+
+```ts
+abstract createNamespace(namespacePath, options?): Promise<CreateNamespaceResponse>
+```
+
+Create a new namespace at the given path.
+
+#### Parameters
+
+* **namespacePath**: `string`[]
+    The namespace path to create.
+
+* **options?**: `Partial`&lt;[`CreateNamespaceOptions`](../interfaces/CreateNamespaceOptions.md)&gt;
+    Creation `mode`
+    ("create" | "exist_ok" | "overwrite") and optional `properties`
+    to attach to the namespace.
+
+#### Returns
+
+`Promise`&lt;[`CreateNamespaceResponse`](../interfaces/CreateNamespaceResponse.md)&gt;
+
+The properties of the
+  created namespace and an optional transaction id.
+
+***
+
 ### createTable()
 
 #### createTable(options, namespacePath)
@@ -230,6 +257,29 @@ Creates a new Table and initialize it with new data.
 
 ***
 
+### describeNamespace()
+
+```ts
+abstract describeNamespace(namespacePath): Promise<DescribeNamespaceResponse>
+```
+
+Describe a namespace, returning its properties.
+
+#### Parameters
+
+* **namespacePath**: `string`[]
+    The namespace path to describe, in
+    parent → child order, e.g. `["analytics", "sales"]`.
+
+#### Returns
+
+`Promise`&lt;[`DescribeNamespaceResponse`](../interfaces/DescribeNamespaceResponse.md)&gt;
+
+The namespace's properties
+  (may be undefined if the namespace has none).
+
+***
+
 ### display()
 
 ```ts
@@ -263,6 +313,36 @@ Drop all tables in the database.
 
 ***
 
+### dropNamespace()
+
+```ts
+abstract dropNamespace(namespacePath, options?): Promise<DropNamespaceResponse>
+```
+
+Drop a namespace.
+
+Use `behavior: "cascade"` to also drop everything contained in the
+namespace (sub-namespaces and tables). The default `"restrict"`
+behavior refuses to drop a non-empty namespace.
+
+#### Parameters
+
+* **namespacePath**: `string`[]
+    The namespace path to drop.
+
+* **options?**: `Partial`&lt;[`DropNamespaceOptions`](../interfaces/DropNamespaceOptions.md)&gt;
+    `mode` ("skip" | "fail"
+    for missing-namespace handling) and `behavior` ("restrict" | "cascade").
+
+#### Returns
+
+`Promise`&lt;[`DropNamespaceResponse`](../interfaces/DropNamespaceResponse.md)&gt;
+
+Any properties returned by
+  the server and an optional transaction id.
+
+***
+
 ### dropTable()
 
 ```ts
@@ -299,6 +379,36 @@ Return true if the connection has not been closed
 
 ***
 
+### listNamespaces()
+
+```ts
+abstract listNamespaces(namespacePath?, options?): Promise<ListNamespacesResponse>
+```
+
+List the immediate child namespaces under the given parent.
+
+Results may be paginated. To retrieve subsequent pages, pass the
+`pageToken` returned by a previous call.
+
+#### Parameters
+
+* **namespacePath?**: `string`[]
+    The parent namespace path. Defaults
+    to the root namespace if omitted.
+
+* **options?**: `Partial`&lt;[`ListNamespacesOptions`](../interfaces/ListNamespacesOptions.md)&gt;
+    Pagination options
+    (`pageToken`, `limit`).
+
+#### Returns
+
+`Promise`&lt;[`ListNamespacesResponse`](../interfaces/ListNamespacesResponse.md)&gt;
+
+Child namespace names and
+  an optional token for fetching the next page.
+
+***
+
 ### openTable()
 
 ```ts