Adds basic unit conversions for attenuator in general_maths folder

[Matt-Carre]

Closes #2038

Begins to work on translating over the calculations behind the attenuator to be available in Dodal. Separates conversions and boundary checks into two different files. Also translates over unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.12%. Comparing base (0beeb31) to head (7618002).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2043   +/-   ##
=======================================
  Coverage   99.11%   99.12%           
=======================================
  Files         327      329    +2     
  Lines       12814    12842   +28     
=======================================
+ Hits        12701    12729   +28     
  Misses        113      113           

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