Add comprehensive tests for playlist service and refactor socket service tests

- Introduced a new test suite for the PlaylistService covering various functionalities including creation, retrieval, updating, and deletion of playlists.
- Added tests for handling sounds within playlists, ensuring correct behavior when adding/removing sounds and managing current playlists.
- Refactored socket service tests for improved readability by adjusting function signatures.
- Cleaned up unnecessary whitespace in sound normalizer and sound scanner tests for consistency.
- Enhanced audio utility tests to ensure accurate hash and size calculations, including edge cases for nonexistent files.
- Removed redundant blank lines in cookie utility tests for cleaner code.

app/main.py

@@ -30,7 +30,7 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
     yield
 
     logger.info("Shutting down application")
-    
+
     # Stop the extraction processor
     await extraction_processor.stop()
     logger.info("Extraction processor stopped")