Also convert attribute units when calling convert_units

[bouweandela]

🚀 Pull Request

Description

Also convert the attributes "actual_range", "valid_max", "valid_min", and "valid_range" on cubes and coordinates.

Closes #6411

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (7fd73e8) to head (28dfd25).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6416   +/-   ##
=======================================
  Coverage   89.80%   89.80%           
=======================================
  Files          90       90           
  Lines       23752    23758    +6     
  Branches     4418     4422    +4     
=======================================
+ Hits        21331    21337    +6     
  Misses       1672     1672           
  Partials      749      749           

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