Update EWA pyproj Proj usage to Transformer

[djhoese]

The pyproj Proj object is deprecated and is not as accurate/explicit as the Transformer interface. I did some of these changes in my #645 branch, but decided that these changes should be their own PR. Unfortunately this also meant that I changed the low-level interfaces of ll2cr to accept a source CRS and a target CRS instead of just the target projection information.

• Closes #xxxx
• Tests added
• Tests passed
• Fully documented

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.98%. Comparing base (eb37fa0) to head (98f20a7).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #648   +/-   ##
=======================================
  Coverage   93.97%   93.98%           
=======================================
  Files          86       86           
  Lines       13536    13543    +7     
=======================================
+ Hits        12721    12728    +7     
  Misses        815      815           

Flag	Coverage Δ
unittests	93.98% <100.00%> (+<0.01%)	⬆️

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[coveralls]

coverage: 93.677% (+0.003%) from 93.674%
when pulling 98f20a7 on djhoese:udpate-ewa-pyproj-transformer
into 1f974b5 on pytroll:main.

[djhoese]

Merging this to get the versioneer fixes and also I'm the primary EWA user anyway so...it should be fine and if not I'll fix it.