Signed parts

[tpazderka]

Parse WSDL for SignedParts and use this knowneldge for signing.

Close #497

[tpazderka]

The test failures are the same as on master branch. This is sort of proof of concept and no extra tests are added. If you find this patch helpful, I will finish up the tests as well.

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.49%. Comparing base (6f421ce) to head (cc81daa).
Report is 197 commits behind head on main.

Files with missing lines	Patch %	Lines
src/zeep/wsdl/bindings/soap.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #747      +/-   ##
==========================================
+ Coverage   89.43%   89.49%   +0.06%     
==========================================
  Files          65       65              
  Lines        4845     4873      +28     
  Branches      850      862      +12     
==========================================
+ Hits         4333     4361      +28     
  Misses        331      331              
  Partials      181      181              

Files with missing lines	Coverage Δ
src/zeep/ns.py	100.00% <100.00%> (ø)
src/zeep/wsdl/definitions.py	79.43% <100.00%> (+0.14%)	⬆️
src/zeep/wsdl/wsdl.py	95.02% <100.00%> (+0.37%)	⬆️
src/zeep/wsse/signature.py	94.87% <100.00%> (+0.53%)	⬆️
src/zeep/wsse/username.py	97.72% <100.00%> (ø)
src/zeep/wsdl/bindings/soap.py	84.21% <50.00%> (ø)

[tpazderka]

Tests are fixed. If you find this patch useful, I will add tests to cover the new changes.

[tpazderka]

Finished up tests. Please review :)

[tpazderka]

Closing this in favor of #1428 which is based on the current master.