feat(python): expose LSM checkpoint and stats on sync RemoteTable (#3961)

## Summary

The sync `RemoteTable` carried `set_lsm_write_spec`,
`unset_lsm_write_spec`, `get_lsm_write_spec`, and `close_lsm_writers`,
but not `checkpoint_lsm`, `flush_lsm`, `compact_lsm`, or
`get_lsm_stats`.

That left the four LSM control methods reachable from `AsyncTable` only.
They are also the four that *only* work against a remote table —
`NativeTable` does not override the `BaseTable` defaults, so on a local
table they return `NotSupported` (`rust/lancedb/src/table.rs:679-701`).
The net effect for sync users:

| | `checkpoint_lsm` / `get_lsm_stats` |
|---|---|
| `LanceTable` (sync, local) | present, but always `NotSupported` |
| `RemoteTable` (sync, remote) | `AttributeError` — method absent |
| `AsyncTable` (remote) | works |

So there was no working sync path at all, despite the Rust `RemoteTable`
implementing every one of these against real endpoints.

## Changes

* Add `checkpoint_lsm`, `flush_lsm`, `compact_lsm`, and `get_lsm_stats`
to `lancedb.remote.table.RemoteTable`, mirroring the delegation style of
their neighbours.
* Correct the docstrings on `set_lsm_write_spec` /
`unset_lsm_write_spec`, which read `"""Not supported on LanceDB
Cloud."""` although `rust/lancedb/src/remote/table.rs:2549-2601`
implements both against `/v1/table/{}/set_lsm_write_spec/` and
`/unset_lsm_write_spec/`. They appear to have been copy-pasted from
`set_unenforced_primary_key` directly above.

No Rust or PyO3 changes — the bindings and the `AsyncTable` methods
already existed. The `Table` ABC is left alone, matching how the
existing `*_lsm_write_spec` methods are declared on the concrete classes
only.

## Tests

Four new tests in `python/python/tests/test_remote_db.py`, against the
existing mock HTTP server:

* `test_get_lsm_stats_sync` — the server payload round-trips into the
dict, and `include_generation_rows` defaults to `False` and is forwarded
when set.
* `test_get_lsm_stats_sync_returns_none_when_lsm_disabled` — a
`{"lsm_stats": null}` envelope yields `None` rather than an error.
* `test_flush_and_compact_lsm_sync` — both are one-shot POSTs answered
`202` with no body.
* `test_checkpoint_lsm_sync` — pins the binding to the endpoints it
drives (`flush_lsm` then `get_lsm_stats`); the convergence loop itself
is already covered in Rust.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

python/python/tests/test_remote_db.py

@@ -1133,6 +1133,131 @@ def test_stats():
         assert res == stats
 
 
+@contextlib.contextmanager
+def lsm_test_table(lsm_handler):
+    """A remote table whose LSM routes are served by ``lsm_handler``.
+
+    ``lsm_handler(request, route)`` is called for ``/v1/table/test/<route>/``
+    where route is one of flush_lsm, compact_lsm, get_lsm_stats, and is
+    responsible for writing the response.
+    """
+    routes = ("flush_lsm", "compact_lsm", "get_lsm_stats")
+
+    def handler(request):
+        match = re.fullmatch(r"/v1/table/test/(\w+)/", request.path)
+        route = match.group(1) if match else None
+        if route in routes:
+            lsm_handler(request, route)
+        elif route == "describe":
+            request.send_response(200)
+            request.send_header("Content-Type", "application/json")
+            request.end_headers()
+            request.wfile.write(b'{"version": 1, "schema": {"fields": []}}')
+        else:
+            request.send_response(404)
+            request.end_headers()
+
+    with mock_lancedb_connection(handler) as db:
+        yield db.open_table("test")
+
+
+def read_json_body(request):
+    content_len = int(request.headers.get("Content-Length"))
+    return json.loads(request.rfile.read(content_len))
+
+
+def send_json(request, payload, status=200):
+    request.send_response(status)
+    request.send_header("Content-Type", "application/json")
+    request.end_headers()
+    request.wfile.write(json.dumps(payload).encode())
+
+
+def test_get_lsm_stats_sync():
+    """The sync wrapper round-trips the server payload into a dict."""
+    bucket = {
+        "shard_id": "b0",
+        "status": "Active",
+        "writer_epoch": 3,
+        "manifest_version": 12,
+        "current_generation": 6,
+        "replay_after_wal_entry_position": 40,
+        "wal_entry_position_last_seen": 42,
+        "generations": [{"generation": 5, "bytes": 1024, "rows": 7}],
+        "compacting": False,
+        "memtables": [
+            {
+                "generation": 6,
+                "rows": 2,
+                "bytes": 64,
+                "batches": 1,
+                "indexes": ["vec_idx"],
+            }
+        ],
+    }
+    seen_bodies = []
+
+    def lsm_handler(request, route):
+        assert route == "get_lsm_stats"
+        seen_bodies.append(read_json_body(request))
+        send_json(request, {"lsm_stats": {"buckets": [bucket]}})
+
+    with lsm_test_table(lsm_handler) as table:
+        assert table.get_lsm_stats() == {"buckets": [bucket]}
+        # Off by default, and forwarded when asked for.
+        assert seen_bodies == [{"include_generation_rows": False}]
+        table.get_lsm_stats(include_generation_rows=True)
+        assert seen_bodies[-1] == {"include_generation_rows": True}
+
+
+def test_get_lsm_stats_sync_returns_none_when_lsm_disabled():
+    """A null envelope means the LSM write path is not enabled, not an error."""
+
+    def lsm_handler(request, route):
+        send_json(request, {"lsm_stats": None})
+
+    with lsm_test_table(lsm_handler) as table:
+        assert table.get_lsm_stats() is None
+
+
+def test_flush_and_compact_lsm_sync():
+    """Both are one-shot POSTs answered 202 with no body."""
+    called = []
+
+    def lsm_handler(request, route):
+        called.append(route)
+        request.send_response(202)
+        request.end_headers()
+
+    with lsm_test_table(lsm_handler) as table:
+        assert table.flush_lsm() is None
+        assert table.compact_lsm() is None
+        assert called == ["flush_lsm", "compact_lsm"]
+
+
+def test_checkpoint_lsm_sync():
+    """Seal, read the watermark, and return once L0 holds nothing.
+
+    The convergence loop itself is covered in Rust; this pins the sync
+    binding to the endpoints it drives.
+    """
+    called = []
+
+    def lsm_handler(request, route):
+        called.append(route)
+        if route == "get_lsm_stats":
+            # An empty L0 yields no target watermark, so the loop is done
+            # after the seal without ever polling compaction.
+            send_json(request, {"lsm_stats": {"buckets": []}})
+        else:
+            request.send_response(202)
+            request.end_headers()
+
+    with lsm_test_table(lsm_handler) as table:
+        assert table.checkpoint_lsm() is None
+        assert called == ["flush_lsm", "get_lsm_stats"]
+
+
 @contextlib.contextmanager
 def query_test_table(query_handler, *, server_version=Version("0.1.0")):
     def handler(request):