src/setup.py: Do not need Cython for sdist or egg_info

[tobiasdiez]

In case src/setup.py is invoked with sdist or egg_info as argument, we do not need to generate code files or cythonize. This also removes the early dependency on Cython. Needed and extracted from #30371.

CC: @mkoeppe @kiwifb @jhpalmieri @isuruf

Component: build

Author: Tobias Diez

Branch/Commit: 17acb7b

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/32673

[tobiasdiez]

Author: Tobias Diez

[mkoeppe]

Reviewer: Matthias Koeppe

[mkoeppe]

comment:4

I've applied a similar change to #29865

[tobiasdiez]

comment:5

Thanks!

[vbraun]

Changed branch from public/build/setup_dist to 17acb7b