hyprland: init module

[nezia1]

This PR adds Hyprland support for hjem-rum.

Things done

• Settings mapped to hyprlang
• Plugins (can either take in a path or a package)
• Automatic environment sourcing (using the user's NixOS config to determine whether or not UWSM is enabled and imports environment the proper way)

Note that the latter will need to be added once hjem gets support for environment variables (feel-co/hjem#16), hence the draft status of this PR.

[nezia1]

Now that sesssion variables have been merged into Hjem, we can make this work. I've been thinking about something though, how do we want to source environment?

I was thinking of doing it at compositor level as this way, we can ensure that it will be properly sourced (also uwsm integration has been implemented). We could also do it at display manager level, but this will require being careful, as DMs environment implementation can be very different (see the arch wiki for reference).

Note that it also differs between Xorg / Wayland, even for the same display manager, so that will have to be taken into account as well. Both approaches would work, the latter would just require carefully sourcing what DM(s) the user is running, and probably a global module but I'm unsure how I would want that to be structured.

Either way, please let me know your thoughts :)

[nezia1]

Added support for setting XDG_* variables related to desktop when not using uwsm, as per https://wiki.hyprland.org/Configuring/Environment-variables/#xdg-specifications.