Respect existing .egg-info files in site packages

[charliermarsh]

Summary

As with other .egg-info and .egg-link distributions, it's easy to support existing .egg-info files. Like pip, we refuse to uninstall these, since there's no way to know which files are part of the distribution.

Closes #4059.

Test Plan

Verify that vtk is included here, which is installed as a .egg-link file:

> conda create -c conda-forge -n uv-test python h5py vtk pyside6 cftime psutil

> cargo run pip freeze --python /opt/homebrew/Caskroom/miniforge/base/envs/uv-test/bin/python
aiohttp @ file:///Users/runner/miniforge3/conda-bld/aiohttp_1713964997382/work
aiosignal @ file:///home/conda/feedstock_root/build_artifacts/aiosignal_1667935791922/work
attrs @ file:///home/conda/feedstock_root/build_artifacts/attrs_1704011227531/work
cached-property @ file:///home/conda/feedstock_root/build_artifacts/cached_property_1615209429212/work
cftime @ file:///Users/runner/miniforge3/conda-bld/cftime_1715919201099/work
frozenlist @ file:///Users/runner/miniforge3/conda-bld/frozenlist_1702645558715/work
h5py @ file:///Users/runner/miniforge3/conda-bld/h5py_1715968397721/work
idna @ file:///home/conda/feedstock_root/build_artifacts/idna_1713279365350/work
loguru @ file:///Users/runner/miniforge3/conda-bld/loguru_1695547410953/work
msgpack @ file:///Users/runner/miniforge3/conda-bld/msgpack-python_1715670632250/work
multidict @ file:///Users/runner/miniforge3/conda-bld/multidict_1707040780513/work
numpy @ file:///Users/runner/miniforge3/conda-bld/numpy_1707225421156/work/dist/numpy-1.26.4-cp312-cp312-macosx_11_0_arm64.whl
pip==24.0
psutil @ file:///Users/runner/miniforge3/conda-bld/psutil_1705722460205/work
pyside6==6.7.1
setuptools==70.0.0
shiboken6==6.7.1
vtk==9.2.6
wheel==0.43.0
wslink @ file:///home/conda/feedstock_root/build_artifacts/wslink_1716591560747/work
yarl @ file:///Users/runner/miniforge3/conda-bld/yarl_1705508643525/work