feat!: rename branch merge to cherry_pick (#3986)

This PR is a **breaking** rename of #3686.

merge reads like git merge w/ three-way, replay history, combine two
lines of work. That is not this API.

This call takes one additive change on a branch and lands it on main.
New column, including a blob column. Main's existing columns are not
rewritten. If it cannot land, you get `status="failed"` and
`diff.errors`, not a merge conflict to resolve.

Cherry-pick is terminology that aligns more with that.

```python
table = db.open_table("images")
table.branches.create("exp")
exp = table.branches.checkout("exp")

exp.add_columns({"tag": "cast('draft' as string)"})

diff = table.branches.diff("exp")
preview = table.branches.cherry_pick("exp", dry_run=True)
result = table.branches.cherry_pick("exp")

if result["status"] == "cherryPicked":
    print("landed at", result["mainVersionAfter"])
elif result["status"] == "failed":
    print(result["diff"]["errors"])
```

### Behavior

- Remote / Enterprise only. Local still NotSupported.
- HTTP 409 is not an exception. It is Ok with status="failed" and
diff.errors (CherryPickError).
- Unknown error / status codes still parse as Unknown.
- Requests are not retried. 409 is final and carries the body.
- Endpoint is POST /v1/table/{id}/branches/cherry_pick/.
- merge_insert and Table.merge are unchanged.

### Testing
- `cargo test -p lancedb --features remote diff_branch`
- `cargo test -p lancedb --features remote cherry_pick`
- `pytest python/python/tests/test_remote_db.py -k cherry_pick`
- node `remote.test.ts` diffs / cherry-picks path

nodejs/__test__/remote.test.ts

@@ -311,7 +311,7 @@ describe("remote connection", () => {
     expect(createIndexBody?.["custom_stop_words"]).toEqual(["the"]);
   });
 
-  it("diffs and merges remote branches", async () => {
+  it("diffs and cherry-picks remote branches", async () => {
     const sampleDiff = {
       fromBranch: "exp",
       parentVersion: 1,
@@ -333,10 +333,9 @@ describe("remote connection", () => {
       changedColumns: [],
       addedIndexes: [],
       removedIndexes: [],
-      mergeable: true,
-      mergeBlockers: [],
+      errors: [],
     };
-    const mergeBodies: Record<string, unknown>[] = [];
+    const cherryPickBodies: Record<string, unknown>[] = [];
 
     await withMockDatabase(
       (req, res) => {
@@ -366,17 +365,16 @@ describe("remote connection", () => {
               .end(JSON.stringify(sampleDiff));
             return;
           }
-          if (path.endsWith("/branches/merge/")) {
-            mergeBodies.push(body);
+          if (path.endsWith("/branches/cherry_pick/")) {
+            cherryPickBodies.push(body);
             const dryRun = body["dry_run"] === true;
             const response = {
-              status: dryRun ? "ready" : "rejected",
+              status: dryRun ? "ready" : "failed",
               diff: dryRun
                 ? sampleDiff
                 : {
                     ...sampleDiff,
-                    mergeable: false,
-                    mergeBlockers: [
+                    errors: [
                       { code: "baseMoved", message: "main has advanced" },
                     ],
                   },
@@ -398,19 +396,19 @@ describe("remote connection", () => {
 
         await expect(branches.diff("exp")).resolves.toEqual(sampleDiff);
 
-        const rejected = await branches.merge("exp");
-        expect(rejected.status).toBe("rejected");
-        expect(rejected.diff.mergeBlockers).toEqual([
+        const failed = await branches.cherryPick("exp");
+        expect(failed.status).toBe("failed");
+        expect(failed.diff.errors).toEqual([
           { code: "baseMoved", message: "main has advanced" },
         ]);
 
-        const preview = await branches.merge("exp", true);
+        const preview = await branches.cherryPick("exp", true);
         expect(preview.status).toBe("ready");
         expect(preview.preview.promotedColumns).toEqual(["tag"]);
       },
     );
 
-    expect(mergeBodies).toEqual([
+    expect(cherryPickBodies).toEqual([
       // biome-ignore lint/style/useNamingConvention: snake_case mandated by the server wire format
       { from_branch: "exp", dry_run: false },
       // biome-ignore lint/style/useNamingConvention: snake_case mandated by the server wire format