feat: transitive extractor for Python requirements

[cuixq]

This PR enables the transitive extractor for Python requirement files. Considering that there is only the native registry client for PyPI, we use that for requirements.txt transitive extractor.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.34%. Comparing base (70074a7) to head (7bc5d73).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1877      +/-   ##
==========================================
+ Coverage   65.28%   65.34%   +0.05%     
==========================================
  Files         164      164              
  Lines       15868    15886      +18     
==========================================
+ Hits        10359    10380      +21     
+ Misses       4845     4843       -2     
+ Partials      664      663       -1     

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[another-rex]

#1846 Going to wait for this one to get merged in first, then we need to do some work to support having both extractor types similar to what that PR does for the pomxml extractor.

[cuixq]

@another-rex do you have idea how long this will take roughly?