pulseaudio backend sometimes get buffer overruns

[sthibaul]

Steps to reproduce

Note sure how, just pasting feedback from @albertotirla

Obtained behavior

Audio buffer overruns

Expected behavior

Audio should flow fine

How to fix

The pulseaudio backend should be revamped to use callbacks to get audio progress notification, rather than little-audio-pushes.

That notably means avoid using libpulse-simple which doesn't support that.