Beckhoff: Engineering units are left at microns by default

As a scientist I would like my Beckhoff to tell me what its engineering units are through IBEX. I identified when commissioning LARMOR that the units for the system were incorrect. The units should be `deg` for LARMOR as it's a rotating bench, however by default we display `um` as the EGU. We should talk to the motion team about how we can add this functionality.

### Acceptance Criteria
_What is the acceptance criteria?_
- [ ] A discussion is had between us and the motion team about adding this functionality.
- [ ] Changes are implemented in tcioc for the units info to propagate to each axis (units may also be different per axis?)
- [ ] Tests are added to make sure this info is propagated correctly

### Extra Information
This information currently isn't stored in the status struct, or subsequently the .tpy file. It may be best to add these through the global struct instead, for example how nAXIS_NUM is added (even though we don't currently use it!)