style: fix ruff formatting issues in conftest.py

- Fix import sorting and organization
- Remove trailing whitespace
- Add proper newline at end of file

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

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

tests/conftest.py

@@ -1,6 +1,7 @@
 """Pytest configuration and fixtures for LEANN tests."""
 
 import os
+
 import pytest
 
 
@@ -8,32 +9,33 @@ import pytest
 def test_environment():
     """Set up test environment variables."""
     # Mark as test environment to skip memory-intensive operations
-    os.environ["CI"] = "true" 
+    os.environ["CI"] = "true"
     yield
-    
 
-@pytest.fixture(scope="session", autouse=True) 
+
+@pytest.fixture(scope="session", autouse=True)
 def cleanup_session():
     """Session-level cleanup to ensure no hanging processes."""
     yield
-    
+
     # Basic cleanup after all tests
     try:
-        import psutil
         import os
-        
+
+        import psutil
+
         current_process = psutil.Process(os.getpid())
         children = current_process.children(recursive=True)
-        
+
         for child in children:
             try:
                 child.terminate()
             except psutil.NoSuchProcess:
                 pass
-                
+
         # Give them time to terminate gracefully
         psutil.wait_procs(children, timeout=3)
-        
+
     except Exception:
         # Don't fail tests due to cleanup errors
         pass