feat(plugins): WaylandIdle

[T1mbits]

Describe your Changes

A plugin to implement the automatic idle detection seen on the official Discord desktop client for Vesktop on Wayland Linux.

A native module needs to be merged into Vesktop for this to work (Vencord/Vesktop#1280). I'm pretty sure loading this plugin on versions and platforms that don't have the module don't break anything, but I've only been able to test versions without the module on linux, so any tests on other platforms would be really appreciated!

I'm not sure if I'm misremembering but I think idling works on Xorg and other platforms, but if it doesn't please let me know so I can add patches to make all platforms idle properly.

Fully tested on NixOS 26.11 unstable with niri 26.04, compatible with CustomIdle.

Some notes:

• The only deviations between stock Discord and this plugin I have observed is that locking doesn't idle discord (as expected, unavoidable wayland design) and that going back online either takes another 10 second polling cycle or the user tabbing/clicking back into Discord. I don't know if the latter is how regular Discord behaves though.
• This will only work on compositors implementing ext-idle-notify-v1. Compositors such as Mutter (used by GNOME) will not work without extending the native module for environment specific implementations. If somebody wants to implement that stuff later it shouldn't be too difficult to do so by modifying the native module.
• Although CustomIdle works fine, changing the idle time requires a full restart of the full Vesktop app, not just Discord, due to having to reload the notifier instance with the new idle time

Checklist before submitting

• I have read the CONTRIBUTING.md file and made sure this pull request complies with it
• This pull request was written by me, and not an AI agent