Enable protontricks python package on Steam Deck by downloading winetricks before

[gmvi]

On my system python protontricks can't find winetricks automatically when installed by uv. Providing it via $WINETRICKS solves the problem without really groking what's going on. So it feels like hotfix quality right now, maybe let's not rush to merge this.

For a temporary workaround the current rewrite branch can be enabled on Steam Deck by downloading a copy of winetricks and pointing $WINETRICKS to it. Once there's a winetricks in ~/.cache/mo2-lint/downloads/, you can point $WINETRICKS to that instead.

Code has been tested against Morrowind and Oblivion via Steam on Steam Deck only.

[gmvi]

I feel silly for assuming this project was using the latest version of protontricks instead of checking 🤦. I was comparing 1.13.1 against 1.14.0, not uv-install vs pip-install.

So, protontricks doesn't come with its own winetricks, and of course it doesn't see the winetricks bundled with flatpak protontricks. So on steam deck we just need to set $WINETRICKS. I also changed the download code to only download winetricks if needed.

Tested up to MO2 on oblivion and up to post-MO2 game launch on morrowind, both via steam on steam deck. I can't get oblivion to run at all right now, I'll have to figure that out.

@Furglitch should I squash these commits into a single one that follows the project format now or just squash-merge after review?