Allow stream API to provide fixed-size requests without compromising latency
Currently, our users of our API need to make a choice between
PA_STREAM_EARLY_REQUESTS which effectively gives
tlength + minreq latency, or use
PA_STREAM_ADJUST_LATENCY and have no real control over the size of data requested in the callback..
Even with the former, we provide no guarantees w.r.t. the size of data requested in the API. It might be worth revisiting how we do this, or even providing some API to emulate a fixed-size callback, which other system audio APIs favour (I believe JACK does this, and likely macOS too).