Use PyQt instead of PySide6

[hefee]

As described in #1871 the hard Qt6 dependency makes it very hard to backport the newer version for Debian. The PyQt abstraction layer makes Debian free to switch Qt6 if everything is packaged correctly.

Currently marked as Draft, as I only made sure that the test suite passes locally.
Closes: #1871

[hefee]

I have tested it to build an run on Debian successfully. So I think it is ready to merge.

[micahflee]

Sorry about taking so long to respond. I'd love to get OnionShare packaged in Debian, but I think we should do two things first:

1. Decide if we want to switch from PySide6 and what the pros (besides Debian support) and cons are, and

2. Much bigger: make sure this works and is packaged properly in Flatpak and Snapcraft in Linux, as well as Windows and macOS. Unfortunately swapping out a dependency like this could take a considerable amount of work for all the platforms we support.

[hefee]

I'm a little bit unsure, what you want to do and what I should do. Can you clarify?. You are the maintainer, so you need to do the decisions. I only can provide you with information...

1) Decide if we want to switch from PySide6 and what the pros (besides Debian support) and cons are, and

pros: * lightweight * give maintainer a easy way to switch Qt versions and different Qt backends, that should make it more easy to get in more distros cons: * an additional abstraction layer * an additional dependency

2) Much bigger: make sure this works and is packaged properly in Flatpak and Snapcraft in Linux, as well as Windows and macOS. Unfortunately swapping out a dependency like this could take a considerable amount of work for all the platforms we support.

I don't have much experience with those platforms, but the qtpy has a test matrix, that looks very promising: https://github.com/spyder-ide/qtpy?tab=readme-ov-file#testing-matrix at least Windows and MacOS should not be an issue.