feat: search multiple query vectors as one query (#1811)

Allows users to pass multiple query vector as part of a single query
plan. This just runs the queries in parallel without any further
optimization. It's mostly a convenience.

Previously, I think this was only handled by the sync Python remote API.
This makes it common across all SDKs.

Closes https://github.com/lancedb/lancedb/issues/1803

```python
>>> import lancedb
>>> import asyncio
>>> 
>>> async def main():
...     db = await lancedb.connect_async("./demo")
...     table = await db.create_table("demo", [{"id": 1, "vector": [1, 2, 3]}, {"id": 2, "vector": [4, 5, 6]}], mode="overwrite")
...     return await table.query().nearest_to([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [4.0, 5.0, 6.0]]).limit(1).to_pandas()
... 
>>> asyncio.run(main())
   query_index  id           vector  _distance
0            2   2  [4.0, 5.0, 6.0]        0.0
1            1   2  [4.0, 5.0, 6.0]        0.0
2            0   1  [1.0, 2.0, 3.0]        0.0
```

python/python/tests/test_remote_db.py

@@ -229,6 +229,17 @@ def test_query_sync_maximal():
         )
 
 
+def test_query_sync_multiple_vectors():
+    def handler(_body):
+        return pa.table({"id": [1]})
+
+    with query_test_table(handler) as table:
+        results = table.search([[1, 2, 3], [4, 5, 6]]).limit(1).to_list()
+        assert len(results) == 2
+        results.sort(key=lambda x: x["query_index"])
+        assert results == [{"id": 1, "query_index": 0}, {"id": 1, "query_index": 1}]
+
+
 def test_query_sync_fts():
     def handler(body):
         assert body == {