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

python/python/tests/test_remote_db.py

@@ -242,8 +242,8 @@ def test_remote_table_branches_sync():
         table.branches.delete("exp")
 
 
-def test_remote_table_branch_merge_defaults_to_execute():
-    merge_bodies = []
+def test_remote_table_cherry_pick_defaults_to_execute():
+    cherry_pick_bodies = []
     diff = {
         "fromBranch": "exp",
         "parentVersion": 1,
@@ -265,8 +265,7 @@ def test_remote_table_branch_merge_defaults_to_execute():
         "changedColumns": [],
         "addedIndexes": [],
         "removedIndexes": [],
-        "mergeable": True,
-        "mergeBlockers": [],
+        "errors": [],
     }
 
     def handler(request):
@@ -276,11 +275,11 @@ def test_remote_table_branch_merge_defaults_to_execute():
         else:
             content_len = int(request.headers.get("Content-Length"))
             request_body = json.loads(request.rfile.read(content_len))
-            merge_bodies.append(request_body)
+            cherry_pick_bodies.append(request_body)
             dry_run = request_body["dry_run"]
             status = 200 if dry_run else 409
             body = {
-                "status": "ready" if dry_run else "rejected",
+                "status": "ready" if dry_run else "failed",
                 "diff": diff,
                 "preview": {"promotedColumns": []},
             }
@@ -292,10 +291,10 @@ def test_remote_table_branch_merge_defaults_to_execute():
 
     with mock_lancedb_connection(handler) as db:
         branches = db.open_table("test").branches
-        assert branches.merge("exp")["status"] == "rejected"
-        assert branches.merge("exp", dry_run=True)["status"] == "ready"
+        assert branches.cherry_pick("exp")["status"] == "failed"
+        assert branches.cherry_pick("exp", dry_run=True)["status"] == "ready"
 
-    assert merge_bodies == [
+    assert cherry_pick_bodies == [
         {"from_branch": "exp", "dry_run": False},
         {"from_branch": "exp", "dry_run": True},
     ]