PR Rollup

[mmstick]

Fixes

• daemon: Early return on a kernel lacking SCHED_DEBUG which causes the service to not start
• daemon: Spawns the pipewire monitoring sub-process with /proc/self/exe
• pipewire: Prevents duplicate threads being spawned to monitor the same pipewire socket

Improvements

• Significant reduction in total memory and CPU consumption
  • Much faster access to process info from a PID lookup
  • Reduced heap allocations in hot paths for new process assignments
  • Added a garbage collection method to be called periodically

Chores

• config: Added schedtool to exceptions
• config: Added gamescope and some game launchers
• daemon: Some additional debug and trace logs
• just: Auto-detect path of execsnoop
• just: Use lld linker if available
• nix: Adds Nix flake

Closes #91

[jacobgkau]

This built fine locally, but has not built successfully on the build server. The logs have been cycled out, so I can't see what the problem was.

[mmstick]

Maybe it'll build on the server this time

[mmstick]

Successfully built this time

[jacobgkau]

Regression testing passed:

• Focus-based assignments are working with the default config (both .debs and Flatpaks).
• Focus-based assignments work with custom values in /etc.
• nice -n # works with the default config.
• A custom profile with no niceness defined still has foreground/background applied.
  • Only foreground niceness is applied in this situation. (Not a regression.)
• A custom profile with a niceness defined inline (under process-scheduler/) works.
• A custom profile with a niceness defined separately (in config.kdl) works.
• Config reloading works with system76-scheduler daemon reload, systemctl reload com.system76.Scheduler.service, and systemctl restart com.system76.Scheduler.service.
• PipeWire integration works; when an app starts playing audio, it's assigned the niceness of the pipewire group and retains it until it's closed. It gets regular foreground/background niceness again when it's relaunched (or sooner if the audio stream stops.)
• After disabling the foreground/background profiles, other profiles still work.

I noticed restarting the daemon (via systemctl restart com.system76.Scheduler.service) is a lot faster now.