cli: don't convert absolute distance in µm

it's confusing to not be able to copy paste, and the 0 in absolute distance might actually
be very far from the current position

Also add log about what's going to happen
cli: simplify error handling

use exceptions to communicate errors internally.
It should have almost not behaviouraly change excepted some slightly different error code.

Also handle cases where the container of scan crash (and keep going).

Also support specifiying the role of a component instead of its name.

Simplify a bit the testing code.

Add testing code for --position and --reference.
driver: add new drivers to __all__

Allows to scan the new type of hardware.
driver tmcm: fix example arguments for the scan response

microsteps are more likely to be ~1nm than 1µm (it's microscopy we are talking about)