Port to qtpy/Qt6

[HotaruBlaze]

This PR has already been talked about a fair bit in discord, So I'll just go over the basics.

There isn't too much of a point to update this other than convenience and that Qt5 is pretty old and reached EoS (End of Support) a couple of days ago.

1. We are using our own fork of python-qtwidgets, This is due to the poor maintainer activity on the repo, as well as issues around the QtPy port they did, that I've had to fix to allow Qt5 and Qt6 Support. If security is a concern, I'd recommend forking my fork of python-qtwidgets and updating requirements.txt.
2. By default everything is now being built assuming Qt6 is the default, This shouldn't actually be an issue, and we can provide Qt5 Specific builds the need to comes up, as its mostly a couple of extra lines and job in GitHub Actions.
3. client/layout/__init__.py got split into two different Qt versions, client/layout/qt5_layout.py and client/layout/qt6_layout.py
4. PyQt5/PyQt6 has been removed from requirements.txt, if you want to build for a specific Qt, you should only have one of those installed, GitHub Actions and the ubuntu install script will default to installing PyQt6.

Note: You can have both PyQt5 and PyQt6 pip packages installed at the same time, however it will currently default to PyQt5 unless you provide it with an argument variable when launching app.py directly. (the bundled app will use whatever Qt it was built for)

[MCMi460]

This is very epic. Thank you for doing this! It had to have been a heck of a monumental project.