Add track-based callback with shuffle per track

[grayxr]

I created an issue with a feature request for essentially doing a track-based callback and shuffle while still tethered to the main clock, so as not to generate multiple instances of uClock and having to synchronize them.

This allows track-based sequencers which use uClock to have track-based control over step counting and shuffle settings. This enables things like applying microtiming/shuffle on steps for individual tracks, rather than microtiming/shuffle on steps for a pattern as a whole.