Use Reference to prevent Device name mangling of undulator and dcm

[shihab-dls]

Fixes #929

Instructions to reviewer on how to test:

1. Check for correct usage of Reference

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.38%. Comparing base (45eb5e0) to head (88be43f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #957      +/-   ##
==========================================
+ Coverage   95.80%   97.38%   +1.57%     
==========================================
  Files         144      143       -1     
  Lines        6179     6079     -100     
==========================================
  Hits         5920     5920              
+ Misses        259      159     -100     

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[rtuck99]

Thanks for this Shihab!
The code changes here look fine, however before merging this, you will need to make changes and raise another PR in mx-bluesky, because the changes here are exposed to calling code in mx-bluesky, and this PR as it stands can't currently be merged without breaking it.

If you run the unit tests and search around in mx-bluesky you will find that there are several places where there are similar dereferences of undulator_dcm.dcm/undulator_dcm.undulator.

You might also want to alter the name of these to make it clear that they are reference wrappers rather than the actual devices - elsewhere where I have added them I have suffixed the names with _ref to make this clear.

A second consideration is whether to make them private by prefixing an underscore, however I think in this case it's ok to leave them public as it's probably both expected and useful to expose the undulator and DCM devices that are backing this composite.

[rtuck99]

See previous comment

[shihab-dls]

Thanks Rob! I've opened up a PR in mx-bluesky amending the exposed references, so I'll tag you and Ollie as reviewers on that one.

[olliesilvester]

Looks good!

Changes have been addressed