ENH: Add source/target CRS to Transformer

[snowman2]

No description provided.

[codecov]

Codecov Report

Merging #976 (4b4a38e) into master (b4ab1d8) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #976      +/-   ##
==========================================
+ Coverage   96.23%   96.24%   +0.01%     
==========================================
  Files          20       20              
  Lines        1752     1758       +6     
==========================================
+ Hits         1686     1692       +6     
  Misses         66       66              

Impacted Files	Coverage Δ
pyproj/transformer.py	94.81% <100.00%> (+0.15%)	⬆️

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