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/src/table.rs

@@ -1940,7 +1940,7 @@ impl Branches {
     }
 
     #[pyo3(signature = (from_branch, dry_run=false))]
-    pub fn merge(
+    pub fn cherry_pick(
         self_: PyRef<'_, Self>,
         from_branch: String,
         dry_run: bool,
@@ -1948,7 +1948,7 @@ impl Branches {
         let inner = self_.inner.clone();
         future_into_py(self_.py(), async move {
             let result = inner
-                .merge_branch(&from_branch, dry_run)
+                .cherry_pick(&from_branch, dry_run)
                 .await
                 .infer_error()?;
             Python::attach(|py| struct_to_wire_py(py, &result))