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.

tests/utils/test_cookies.py

@@ -1,6 +1,5 @@
 """Tests for cookie utilities."""
 
-
 from app.utils.cookies import extract_access_token_from_cookies, parse_cookies