Library should not enforce real-time priority

The library should not enforce real-time priority for its threads. That should be the responsibility of the frontend program.

Reason: In general, I would not expect such behavior from a library unless explicitly asked for. In my opinion, that’s in the same category as calling abort().

On some Linux desktop systems, for instance, even non-root users may have permission to set real-time priority on a process — typically when configured to run JACK for low-latency audio.

This is a problem because SVT-AV1 will render such a desktop system nearly unusable: it will take CPU time away from even input processing (keyboard/mouse).

Also, setting real-time priority on Linux has completely negligible impact on encoder performance.