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 81.53%. Comparing base (ae023d1) to head (a516db0).
Report is 17 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    81.98%   81.53%   -0.46%     
===========================================
  Files           25       26       +1     
  Lines         5224     5263      +39     
  Branches      1257     1259       +2     
===========================================
+ Hits          4283     4291       +8     
- Misses         633      657      +24     
- Partials       308      315       +7     

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[ocefpaf]

Closing this in favor of #1118