style: run ruff format on modified files

- Format diskann_backend.py and conftest.py according to ruff standards

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/leann-backend-diskann/leann_backend_diskann/diskann_backend.py

@@ -477,6 +477,7 @@ class DiskannSearcher(BaseSearcher):
         # Force garbage collection to ensure C++ objects are destroyed
         try:
             import gc
+
             gc.collect()
         except Exception:
             pass

tests/conftest.py

@@ -39,4 +39,3 @@ def cleanup_session():
     except Exception:
         # Don't fail tests due to cleanup errors
         pass
-