BeamStripping: use unit meter internally to avoid conversions

The following discussion from !368 (merged) should be addressed:

• @ext-calvo_p started a discussion:

  This modification will affect also to BeamStripping. I will update units in a new issue

For #357 the beam stripping element should use unit m instead of mm

added Enhancement label

changed the description

mentioned in merge request !368 (merged)

mentioned in commit 73edf13f

closed via merge request !368 (merged)

marked the checklist item @ext-calvo_p started a discussion: as completed

marked this issue as related to #357