RFE: port to cython 3.x

[kloczek]

As 27f9a99 locks cython version to older version and now pyyaml is one of the only few remaining modules still not possible to use with cython 3.x it would be good to that version.

[cpcloud]

This blocks a fair number of applications and libraries from creating source builds that include, say, the latest scikit-learn.

You have to:

• install cython<3
• build pyyaml
• uninstall cython<3
• install cython>=3
• build any dependencies that depend on cython>=3

It also makes creating development environments difficult, since there's no reasonable way to have two different versions of the same package in an environment.

[kloczek]

Just FTR: I have packaged +1.25k python modules as rpm packages. Amongst those

[tkloczko@pers-jacek SPECS]$ grep 'BuildRequires:.*python3dist(cython)' *spec -l | wc -l
66

needs cython' to build. ATM pyyamlis ONLY modules in that set which is not possible to build usingcython` 3.x 😞