Add support for Windows

[dgsasha]

• [x] Fix excessive memory consumption. I don't really think there's a memory leak, but the memory usage is extremely high, like 500mb+. At a certain point it starts getting released back to the OS which is a good sign, but GTK4 seems to use way more memory than it should on windows. One possible change that should be made is the windows that are stored in memory after they are closed maybe should be destroyed instead of hidden. Not sure if this would be better or worse.
• [x] Use the windows file picker. The GTK file picker is a little buggy on windows and looks out of place so maybe switching to a windows one would be better.
• [x] Fix notification actions. I can't get the notification actions to activate the app through the command line, so right now the notifications do nothing when clicked. Unsending notifications also doesn't work.
• [x] Add CI for windows builds.

[dgsasha]

This should be ready to merge once I test that this didn't break anything on Linux.

[dgsasha]

[dgsasha]

This is exceptionally laggy under UWP for some reason, gonna have to work on it some more. Other than that everything works fine, but I am very confident I broke things on linux lol.

[dgsasha]

I should have known, microsoft just doesn't allow the use of anything other than directx on UWP, even for desktop apps that don't release on Xbox. I think this will fix it though.

Edit: Seems like it increases memory usage but whatever, this is the only way I'm getting things working. Maybe I should give up on the microsoft store tbh.

[dgsasha]

Need to test this on linux, other than that it should be good to go. Merging tomorrow and releasing a new beta tomorrow.