There is an updated pull request by tornaria against master on the void-packages repository

https://github.com/tornaria/void-packages sagemath-cython3
https://github.com/void-linux/void-packages/pull/45887

sagemath: use cython 3
#### Testing the changes
- I tested the changes in this PR: **briefly**

Since https://github.com/sagemath/sage/pull/36109 was merged upstream, it's now almost trivial to build sagemath with cython 3. This PR is pretty straightforward to understand:

 - commit 7f8e6514ffa54449a80e01fbae7f9355a7739a46 rebuilds `python3-pplpy` using cython 3. Nothing fancy here and this commit was already tested and only dropped since it turned out it had to be built with the same version of cython as sagemath itself.
 - commit df0d21871ce850efea3fc01f19a3d9e8c0d5f0d4 is just adding a few patches to sagemath, switching to cython 3, and bumping.

Description of added patches:
1. patch `36109-00pre.patch`: this is hand picked trivial patch that allows us to apply https://github.com/sagemath/sage/pull/36109 cleanly on 10.1 (since that PR is based on 10.1.beta0). All changes are comments!
2. patch `36109-prepare_for_cython_3.0.patch`: this is long, taken verbatim from https://github.com/sagemath/sage/pull/36109.diff, and is already merged.
3. patch `build-cython3.patch`: this is 2 lines changed plus 4 legacy build options added to cython setup.
4. patch `fix-doctest-cython3.patch`: this is a few fixes in doctests to accomodate minor changes in cython output (`__repr__` for cython classes, functions, and generators).

CC: @ahesford 

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A patch file from https://github.com/void-linux/void-packages/pull/45887.patch is attached