Cython 3.1+ fixes

[greglucas]

This fixes the errors that came up during Cython3.1a testing. I'm not a Cython expert by any means, so let me know if there is a better way to handle any of these. Do you want to add a test/workflow for upcoming Cython releases?

Test with this nightly wheel release install locally:

pip install --upgrade --pre --only-binary :all: -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple cython numpy
pip install .
python -m pytest

• Closes Upcoming Cython 3.1 str <-> bytes errors #1451

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.50%. Comparing base (efa3faa) to head (ad516d1).
Report is 55 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1452      +/-   ##
==========================================
+ Coverage   96.40%   96.50%   +0.09%     
==========================================
  Files          20       20              
  Lines        1810     1830      +20     
==========================================
+ Hits         1745     1766      +21     
+ Misses         65       64       -1     

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[snowman2]

Do you want to add a test/workflow for upcoming Cython releases?

Yes, that change is welcome.

[greglucas]

Do you want to add a test/workflow for upcoming Cython releases?

Yes, that change is welcome.

I added it to the PROJ_latest workflow to just install the latest Cython there as well. Let me know if you want it as an isolated workflow instead.

[snowman2]

Thanks @greglucas 👍