Enhance MockSuperConductingMagnetController to be configurable

[oliwenmandiamond]

Fixes #2188

Instructions to reviewer on how to test:

1. Check implementation makes sense
2. Check tests pass

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 99.33%. Comparing base (e8b29c8) to head (09a1276).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2189   +/-   ##
=======================================
  Coverage   99.33%   99.33%           
=======================================
  Files         367      367           
  Lines       14379    14389   +10     
=======================================
+ Hits        14284    14294   +10     
  Misses         95       95           

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[oliwenmandiamond]

Required for DiamondLightSource/sm-bluesky#363