If the MMU receives a command LoadFilament with a slot number SL we reject
the command to avoid moving the selector (effectively cutting the piece of filament present in FINDA).
That includes the scenario when the selector is standing at the very same slot SL, because the filament could be held by the printer (i.e. loaded in the nozzle).
There is one special case though - same slot AND filament load state == InSelector (it MUST NOT be anywhere farther)
That implies changing motor's mode from SpreadCycle into StealtMode (or vice versa)
requires a stand still MMU with no other command (i.e. motor moves) being performed.
This elegantly solves the synchronization problem of TMC2130 mode change, as it results
in severe jerking while a motor is moving.
The change in protocol is minimal - M0/M1 first return `M0 A` (accepted) and another `Q0` then
returns `M0 F` (finished). The MK4 counterpart may ignore the additional report if necessary
as the mode change is done immediately (shortly after responding with `M0 A`)
Guðni Már Gilbert
D.R.racer