Migrate usages of pyproj Proj to pyproj Transformer

[djhoese]

This PR switches from using pyproj's old Proj interface to the newer Transformer class. Transformers should have better overall handling of more complex projection transformation.

One note is that I did have to add special handling of CRSes with prime meridian shifts (+pm=180) to make get_lonlats return what it used to. That is, lon/lats on a prime meridian 0 CRS.

CC @larsbuntemeyer

• [x] Closes #527
• [ ] Tests added
• [x] Tests passed
• [x] Passes git diff origin/main **/*py | flake8 --diff
• [x] Fully documented

[codecov[bot]]

Codecov Report

Merging #532 (09fcc76) into main (2a6d769) will decrease coverage by 0.09%. The diff coverage is 97.22%.

@@            Coverage Diff             @@
##             main     #532      +/-   ##
==========================================
- Coverage   94.34%   94.26%   -0.09%     
==========================================
  Files          82       82              
  Lines       13026    13052      +26     
==========================================
+ Hits        12290    12303      +13     
- Misses        736      749      +13     

Flag	Coverage Δ
unittests	94.26% <97.22%> (-0.09%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pyresample/utils/proj4.py	98.86% <93.75%> (-1.14%)	:arrow_down:
pyresample/_spatial_mp.py	83.70% <100.00%> (+0.75%)	:arrow_up:
pyresample/geometry.py	87.64% <100.00%> (+0.05%)	:arrow_up:
pyresample/test/test_geometry/test_area.py	99.21% <100.00%> (+<0.01%)	:arrow_up:

... and 1 file with indirect coverage changes

[larsbuntemeyer]

Thanks for fixing this @djhoese !

[coveralls]

coverage: 93.836% (-0.03%) from 93.864% when pulling 09fcc7658c618276b19dbc1118a243bf1c047f48 on djhoese:bugfix-pyproj-transformer into 82b9373a03ae979985e18ef1eaa25ea04a0db530 on pytroll:main.