-Migration to PyQT 6.
-Added option to keep buffer and sample rate saved.
-Added auto-start option (should work straight away with Arch package and flatpak and deb. For pyinstaller binary and AppImage, 'Exec' entry in ~/.config/autostart/cable-autostart.desktop has to be amended for that to work).
-'Default App' toggle should now remember its state.
-Removed file lock, as it was causing too much trouble.