Some PyPI origins declare sdist archives as Python eggs files, a legacy format used before Python wheels became
the standard for distributing Python modules, see Djangy 0.7 for instance.
Those files are simple ZIP archives and contain a PKG-INFO file located in an EGG-INFO folder but currently
they cannot be processed by the PyPI loader.
We should add support for loading those type of artifacts into the archive by:
- adding support to uncompress files with .egg extension in swh.core.tarball
- adapting swh.loader.package.pypi.loader.extract_intrinsic_metadata to parse the EGG-INFO/PKG-INFO file