feat: Enhance playlist management and GUI logic

- Improved playlist item fetching by adding robust pagination and low-level request hooks for better testing and flexibility.
- Refactored track ID extraction logic into reusable helpers for clarity.
- Improved initialization for dialog components to avoid circular dependencies in the GUI.
- Added new unit tests to validate playlist operations, including track addition/removal and API integration.
- Updated metadata functions to simplify dictionary access using `.get` for better readability.
- Ensured PySide6 system dependencies are installed in GitHub Actions to address CI compatibility issues.
- Streamlined UI package initialization to improve modularity and robustness of imports.

tidal_dl_ng/gui/playlist.py

@@ -25,7 +25,7 @@ class GuiPlaylistManager:
 
     def __init__(self, main_window: "MainWindow"):
         """Initialize the playlist manager."""
-        self.main_window: "MainWindow" = main_window
+        self.main_window: MainWindow = main_window
         self.settings = main_window.settings
 
     def init_ui(self):