Fix CI errors: linting, type checking, and tests

- Fix import sorting in test_instruments.py (ruff I001)
- Install pandas-stubs for mypy type checking
- Add garbage collection cleanup to repository test fixtures
- Prevent Windows file locking errors in tempfile cleanup

All CI checks now passing: lint, type check, and all 244 tests.

tests/unit/test_repository.py

@@ -22,7 +22,13 @@ def temp_db():
 @pytest.fixture
 def repository(temp_db):
     """Create a repository instance for testing."""
-    return SQLiteRepository(temp_db)
+    import gc
+    repo = SQLiteRepository(temp_db)
+    yield repo
+    # Ensure all connections and file handles are closed before cleanup
+    # This is critical on Windows to prevent PermissionError
+    del repo
+    gc.collect()
 
 
 def test_create_run(repository):
@@ -235,6 +241,7 @@ def test_multiple_results(repository):
 
 def test_custom_measurements_dir(temp_db):
     """Test using a custom measurements directory."""
+    import gc
     with tempfile.TemporaryDirectory() as tmpdir:
         measurements_dir = Path(tmpdir) / "custom_measurements"
         repo = SQLiteRepository(temp_db, measurements_dir=measurements_dir)
@@ -254,6 +261,10 @@ def test_custom_measurements_dir(temp_db):
         expected_path = measurements_dir / f"run_{run_id}" / "measurements.parquet"
         assert expected_path.exists()
 
+        # Clean up repository before temp directory cleanup
+        del repo
+        gc.collect()
+
 
 def test_parquet_schema(repository):
     """Test that Parquet file has correct schema."""