fix: hybrid search minimum_nprobes(0) silently no-ops instead of raising (#3770)

## Summary

`LanceHybridQueryBuilder._create_query_builders()` checked
`self._minimum_nprobes` for truthiness instead of `is not None` — the
very next line correctly checks `is not None` for
`self._maximum_nprobes`. Since `0` is falsy in Python,
`.minimum_nprobes(0)` on a hybrid query silently dropped the value
instead of forwarding it to the vector sub-query, where it would raise
the same `ValueError` a plain vector query raises for the same input
(`minimum_nprobes must be greater than 0`, validated in
`rust/lancedb/src/query.rs` and covered for the plain-query path by
`test_invalid_nprobes_sync`).

Fixes #3766

## Change

One-line fix: `if self._minimum_nprobes:` → `if self._minimum_nprobes is
not None:`, matching the existing `maximum_nprobes` check right below
it.

## Test plan

- [x] New regression test
`test_hybrid_query_minimum_nprobes_zero_raises` in
`python/python/tests/test_hybrid_query.py`
- [x] `uv run --extra tests pytest python/tests/test_hybrid_query.py
-vv` — 13 passed
- [x] `uv run --extra dev ruff format` / `ruff check` — clean

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

python/python/lancedb/query.py

@@ -2697,7 +2697,7 @@ class LanceHybridQueryBuilder(LanceQueryBuilder):
             self._fts_query.phrase_query(True)
         if self._distance_type:
             self._vector_query.metric(self._distance_type)
-        if self._minimum_nprobes:
+        if self._minimum_nprobes is not None:
             self._vector_query.minimum_nprobes(self._minimum_nprobes)
         if self._maximum_nprobes is not None:
             self._vector_query.maximum_nprobes(self._maximum_nprobes)

python/python/tests/test_hybrid_query.py

@@ -123,6 +123,19 @@ async def test_async_hybrid_query_default_limit(table: AsyncTable):
     assert texts.count("a") == 1
 
 
+def test_hybrid_query_minimum_nprobes_zero_raises(sync_table: Table):
+    # minimum_nprobes(0) must raise the same validation error a plain vector
+    # query raises, not silently no-op because 0 is falsy.
+    with pytest.raises(ValueError, match="minimum_nprobes must be greater than 0"):
+        (
+            sync_table.search(query_type="hybrid")
+            .vector([0.0, 0.4])
+            .text("dog")
+            .minimum_nprobes(0)
+            .to_arrow()
+        )
+
+
 def test_hybrid_query_distance_range(sync_table: Table):
     reranker = RRFReranker(return_score="all")
     result = (