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_query.py

@@ -2138,6 +2138,12 @@ def test_ensure_vector_query_nested_empty_list():
         ensure_vector_query([[]])
 
 
+@pytest.mark.parametrize("query", [[], np.array([], dtype=np.float32)])
+def test_vector_query_builder_empty_vector(table, query):
+    with pytest.raises(ValueError, match="^Query vector must not be empty$"):
+        LanceVectorQueryBuilder(table, query, "vector")
+
+
 def test_fast_search(tmp_path):
     db = lancedb.connect(tmp_path)