Feature request: convert motion to queue with hardware timers

[rdpeake]

One of the hard parts with working with the mmu2 is that the hardware becomes none responsive once any motion is triggered. Borrowing from the marlin code (and assuming the CPU used on the main board is capable of doing so) is it possible to use the timers interrupt service routine to schedule 'the next motion' for the steppers allowing the serial coms and other such debugging activities to run on the main thread. Make it very easy to debug the finda probe in normal operation as the printer could be easily requesting it whilst the load and unload are happening - probably a bunch of other improvements that could be handy so far as stability go as well, don't have to hit and hope quite so much.

Is the mmu2 control board capable of using a timer isr to advance it's steppers and leave main loop for serial coms?