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)
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