Buffer vs spool loading speed

[thisiscam]

This PR adds an optional config entry long_moves_speed_from_spool. By default, this value is the same as long_moves_speed and the behavior is same as before. If long_moves_speed_from_spool is provided, ERCF will pull at a lower speed if the filament could be directly pulling from the spool.

In practice, this means that the first load from a gate (since last ERCF gates' states reset) will be a slow move, and the rest of the loading moves from the gate will be fast, where we assume the filament is in some kind of filament buffer.

This allows greater torque of the gear stepper and avoids loosing steps at high speed.

[thisiscam]

I also fixed a problem where load_bowden appears to be using gear_stepper.velocity instead of fast_move_speed.