fix(python): reject empty query vectors before column inference (#4415)

Empty list and NumPy vector queries were validated too late: local
search inferred a vector column first, producing misleading schema
errors, while remote search indexed `vector[0]` and raised `IndexError`.

Add a shared empty-vector check before column inference and query
creation, and validate direct vector-builder inputs. Local and remote
sync search now raise `ValueError: Query vector must not be empty` for
these inputs.

Validation:

- All 26 new regression cases failed on the original code and pass with
the fix, covering list/NumPy inputs, automatic/explicit vector search,
inferred/explicit column names, one/two local vector columns, and remote
search before query submission.
- After merging current `main`, all 32 focused cases passed, covering
these regressions and upstream async searches without a query.
- The query, table, remote, utility, hybrid-query, and database suites
passed in the rebuilt uv environment: 541 passed, 1 skipped, 1 slow test
deselected.
- `ruff check .`, `ruff format .`, and `cargo fmt --all` passed from the
repository root.

Fixes #4389

<!-- lance-gatekeeper-fix:v1 agent=f1f4875090ef391bb1aa912dd54026dc
generation=1 -->

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>

python/python/tests/test_remote_db.py

@@ -16,6 +16,7 @@ import uuid
 from packaging.version import Version
 
 import lancedb
+import numpy as np
 from lancedb.conftest import MockTextEmbeddingFunction
 from lancedb.query import AsyncQuery, ColumnOrdering
 from lancedb.remote import ClientConfig
@@ -1592,6 +1593,20 @@ def test_query_sync_empty_query():
         assert data == expected
 
 
+@pytest.mark.parametrize("query", [[], np.array([], dtype=np.float32)])
+@pytest.mark.parametrize("vector_column_name", [None, "vector"])
+@pytest.mark.parametrize("query_type", ["auto", "vector"])
+def test_query_sync_empty_vector(query, vector_column_name, query_type):
+    def handler(body):
+        pytest.fail("An empty query vector must be rejected before sending a query")
+
+    with query_test_table(handler) as table:
+        with pytest.raises(ValueError, match="^Query vector must not be empty$"):
+            table.search(
+                query, vector_column_name=vector_column_name, query_type=query_type
+            ).limit(3).to_arrow()
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize("search_kwargs", [{}, {"query": None}])
 async def test_async_search_without_query(search_kwargs):