Refactor YouTube Playlist Downloader

- Moved main execution logic to cli.py and updated imports accordingly.
- Created a new __init__.py file to export the main function from the cli module.
- Implemented the PlaylistDownloader class in downloader.py to handle playlist downloading logic.
- Added ConfigLoader class in config.py to manage configuration settings.
- Introduced PlaylistManager class in manager.py to manage multiple playlists.
- Updated encoding handling for Windows in the main execution block.
- Removed redundant code and improved overall structure for better readability and maintainability.

ytplaylist/__init__.py

@@ -0,0 +1,4 @@
+"""ytplaylist package exports"""
+from .cli import main
+
+__all__ = ["main"]