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/utils/audio.py

@@ -32,4 +32,4 @@ def get_audio_duration(file_path: Path) -> int:
         return int(duration * 1000)  # Convert to milliseconds
     except Exception as e:
         logger.warning("Failed to get duration for %s: %s", file_path, e)
-        return 0
+        return 0