py-pip-requirements-parser: update to 32.0.1.

v32.0.1
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Ensure all tests pass correctly.
Adopt latest skelton

Add new RequirementsFile.from_string() convenience factory method

Vendor LegacyVersion from pre V2 packaging. Otherwise packaging v2 broke
this library and its dependencies.

v32.0.0
-------

Emergency pin of packaging to version under 22.
This breaks this library and its dependents otherwise

(wiz)