Use pint instead of cf_units

[ocefpaf]

There is still a long road ahead but we can probably ditch the heavy udunits2 dependency if this works.

xref.: Ouranosinc/xclim#1788

[codecov]

Codecov Report

Attention: Patch coverage is 69.38776% with 15 lines in your changes missing coverage. Please review.

Project coverage is 81.33%. Comparing base (3213f6d) to head (f4737d6).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
compliance_checker/units.py	61.53%	15 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1094      +/-   ##
===========================================
- Coverage    81.79%   81.33%   -0.46%     
===========================================
  Files           25       26       +1     
  Lines         5223     5262      +39     
  Branches      1256     1258       +2     
===========================================
+ Hits          4272     4280       +8     
- Misses         644      668      +24     
- Partials       307      314       +7     

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