I09 Add reverse function to calculate energy from gap, harmonics and lookuptable.

[Villtord]

Fixes DiamondLightSource/sm-bluesky#222

Instructions to reviewer on how to test:

1.Confirm tests run without errors

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 99.09%. Comparing base (bdebc72) to head (d113b8b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1712   +/-   ##
=======================================
  Coverage   99.08%   99.09%           
=======================================
  Files         275      275           
  Lines       10099    10114   +15     
=======================================
+ Hits        10007    10022   +15     
  Misses         92       92           

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