Skipping a few initial chunks in updating playback delay averages to allow "warming up" the Processing thread

[pavhofman]

This is just an idea to discuss. Since it's possible that processing the first one (or several) chunks does different things than for the subsequent chunks ("warming up" the structures etc.), it may take a different time, resulting in skewed delay for the averaging. Maybe averaging the delay in the Playback thread should skip these chunks.

Something like this: https://github.com/pavhofman/camilladsp/commit/6fa80a2ee11f03e49886383fb86b2efa458fcf81