Slower loading speed is necessary for precise detection
of filament sensor trigger and starting rotation of the E-motor.
Experimentally it turned out speeds above 80mm/s tend to cause timing issues
(sometimes one can hear a crack as MMU' or the printer's drive gears
slip while pushing the filament).
Such a timing issue then causes blobs in purge towers.
On the other hand - 80mm/s for the fast part of filament load
seems not only absolutely reliable, but also very quiet.
120mm/s for unload is much louder (we may slow it down later)
Solves an interesting tiny issue introduced in the previous commits.
When we start with the filament in selector, the corresponding LED
is set to ON. However, all of the logic state machines only operated
on the LED pair of the active slot -> the starting LED may have been
left ON in some edge cases.
Now, this is resolved by clearing all other LEDs except for the active
slot where appropriate.
Besides Unload Filament, which only operates on active slot, all other
top level state machines check the validity of the command's parameter.
If the parameter is out of range for available slots, they return
ErrorCode::INVALID_TOOL now.
D.R.racer
3d-gussner