Proton-CachyOS: Remove deprecated Type Hinting

[sonic2kk]

This PR removes the deprecated type hints from the typing module. They exist sprinkled throughout the codebase, and should be removed, so I don't mean to single out this ctmod. I spotted this as I'm eyeing some changes to help it further inherit from the GE-Proton ctmod in the future, so I was in and around here and noticed it. I have also removed a couple of unused imports from this Ctmod.

I also added the @override annotation to methods we override from GE-Proton, which we currently don't do elsewhere in the codebase, although it is something I also did in #498. Like with removing the old deprecated type hints, I hope to go through and add these around the codebase where relevant (I think only the Ctmods, maybe there's a Qt component we subclass for the Shortcut Editor but I'm not 100% sure).

[sonic2kk]

Actually, this annotation may only be available in Python 3.10. Looking at the PEP (PEP 698), I believe it's only in 3.12, but we currently build against Python 3.10 for the AppImage. Python 3.10 is still getting security updates until October 31st 2026, so it is not really worth bumping just to get this extra feature.

I should really have my ProtonUp-Qt virtualenv based on at Python 3.10, not 3.12... Would need to test this against 3.12 to make sure this works, although looking at the docs, the Python 3.10 docs don't mention @override, but the Python 3.12 docs do.

Will need to confirm if this decorator is actually available to us.