ENH: Added support to pickle Transformer

[snowman2]

• Closes Cannot pickle TransformerLocal object #1058
• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

[codecov]

Codecov Report

Merging #1060 (044b550) into main (57ecfc8) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1060      +/-   ##
==========================================
+ Coverage   96.30%   96.31%   +0.01%     
==========================================
  Files          20       20              
  Lines        1785     1791       +6     
==========================================
+ Hits         1719     1725       +6     
  Misses         66       66              

Impacted Files	Coverage Δ
pyproj/transformer.py	94.97% <100.00%> (+0.14%)	⬆️

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