Respect and enable uninstalls of existing .egg-info packages

[charliermarsh]

Summary

Users often find themselves dropped into environments that contain .egg-info packages. While we won't support installing these, it's not hard to support identifying them (e.g., in pip freeze) and uninstalling them.

Closes #2841.
Closes #2928.
Closes #3341.

Test Plan

Ran cargo run pip freeze --python /opt/homebrew/Caskroom/miniforge/base/envs/TEST/bin/python, with an environment that includes pip as an .egg-info (/opt/homebrew/Caskroom/miniforge/base/envs/TEST/lib/python3.12/site-packages/pip-24.0-py3.12.egg-info):

cffi @ file:///Users/runner/miniforge3/conda-bld/cffi_1696001825047/work
pip==24.0
pycparser @ file:///home/conda/feedstock_root/build_artifacts/pycparser_1711811537435/work
setuptools==69.5.1
wheel==0.43.0

Then ran cargo run pip uninstall, verified that pip was uninstalled, and no longer listed in pip freeze.

[samypr100]

Also closes #2841

[charliermarsh]

Thanks! Added.

[hauntsaninja]

Should the metadata method read from PKG-INFO?

[charliermarsh]

Yes good call, thanks.