Properly handle systemd signals

[RodoMa92]

Please tick as appropriate:

• I have tested this code on a steam deck or on a PC
• My changes generate no new errors/warnings
• This is a bugfix/hotfix
• This is a new feature

Description

This fixes issue: #683

Properly handle signals from systemd, now it should shutdown gracefully.

Need testing.

Sorry for the noise, forgot to change git username from previous tested stuff.

[milroneth]

I tried switching to this to test, but I still got this:

(deck@stoneship ~)$ time sudo systemctl stop plugin_loader

real    0m57.605s
user    0m0.018s
sys     0m0.011s

And here's my journalctl log this time: Stopping SteamDeck Plugin Loader LOG.txt

I notice that both Fantastic and PowerTools take 5 seconds to unload, like they have their own timeouts, and the total time is weirdly 57 seconds now, though it's exactly 45 seconds just before plugin_loader.service: State 'final-sigterm' timed out. Killing.

[AAGaming00]

It already catches these signals though, it just gets stuck shutting down

[RodoMa92]

It already catches these signals though, it just gets stuck shutting down

Oh, lol. Is the core or the plugins the issue then?

[AAGaming00]

Might be core, @suchmememanyskill is looking into it

[RodoMa92]

Closing in favour of #695