ENH: Add Transformer.transform_bounds

[snowman2]

• Related to would it be possible to have the CRS bounds in its original unit ?  #809
• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

[snowman2]

Seems like Windows doesn't like the current implementation. Works on linux 🤷‍♂️

[codecov]

Codecov Report

Merging #810 (bfb43d0) into master (ee5b86f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #810   +/-   ##
=======================================
  Coverage   95.14%   95.14%           
=======================================
  Files          21       21           
  Lines        1647     1649    +2     
=======================================
+ Hits         1567     1569    +2     
  Misses         80       80           

Impacted Files	Coverage Δ
pyproj/transformer.py	95.87% <100.00%> (+0.04%)	⬆️

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[snowman2]

There are some edge cases mentioned here: OSGeo/PROJ#2616. But, I think this is a good enough start.