#2 Update namespace package packaging

[Theodore Ni]

Hello!

I work on packaging Python packages in nixpkgs, and I was wondering if it would be possible to reproduce the approach in this commit in ruamel-yaml in ruamel-base as well.

We build a wheel and, since that change in ruamel-yaml, setuptools creates one in which ruamel.yaml is an implicit namespace package. On the other hand, ruamel-base still uses setuptool's legacy namespace package code path. I am not entirely sure what's going on, but this mixture causes issues with nixpkgs's approach of putting together a PYTHONPATH.

I wrote about my findings about this in the context of another package that mixed implicit and legacy namespaces here: https://github.com/pypa/setuptools/discussions/3991