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 99.13%. Comparing base (c3e106f) to head (1383712).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2043   +/-   ##
=======================================
  Coverage   99.13%   99.13%           
=======================================
  Files         333      335    +2     
  Lines       13021    13062   +41     
=======================================
+ Hits        12908    12949   +41     
  Misses        113      113           

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[oliwenmandiamond]

The standard for dodal for tests is "mirror the file structure of the src folder with the corresponding code files. Use the test_*.py naming convention for test files."

Can you please update your tests accordingly?

https://diamondlightsource.github.io/dodal/main/how-to/write-tests.html

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