ChooseInt: fix the priority of 24-bit integers, but keep them disabled due to what looks like a compiler bug
MotionPlanner: optimize ISR.
Instead of moving executed commands to the free list, have the free list continue into the command list.
MotionPlanner: optimization.
When not stepping, use m_last_committed to allow directly appending new stepper commands to the free list before,
instead of fixing the free list to continue into the command list just before before stepping begins.