DEPS: Bump cython 3.0
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Looks pretty good. Are all of these changes required to make Cython 3.0 work or are some of the signature changes general cleanups that made sense to bundle?

@Dr-Irv FYI in case this impacts pandas-stubs > Looks pretty good. Are all of these changes required to make Cython 3.0 work or are some of the signature changes general cleanups that made sense to bundle?
> 
> @Dr-Irv FYI in case this impacts pandas-stubs

Yeah, it turns out our stubs are horrendously outdated. I guess Cython 3.0 exposes the annotation information, so stubtest is complaining now. > 
> @Dr-Irv FYI in case this impacts pandas-stubs

We're not that good in keeping the PYI files in the pandas source and the PYI files in `pandas-stubs` in sync.  There's some related discussion here:  https://github.com/pandas-dev/pandas-stubs/issues/128

One of the issues here is that the pandas source has things in its PYI files for "private" methods - i.e., methods and classes that are not documented but are used to type check the pandas source.  The philosophy on pandas-stubs is to only provide stubs for documented methods and classes - although we may be missing some documented methods/classes that should be in the pandas-stubs, and there are also ones that are in pandas-stubs that are not documented.  Cleaning that up is a long term goal. Do we really want to include this bump in the 2.1.0 release? AFAIK Apache Arrow will adapt Cython 3.0.0 in their 14.0.0, but they do not release 13.0.0 yet, meaning the integration with Apache Arrow will not work, right?  > Do we really want to include this bump in the 2.1.0 release? AFAIK Apache Arrow will adapt Cython 3.0.0 in their 14.0.0, but they do not release 13.0.0 yet, meaning the integration with Apache Arrow will not work, right?

We don't compile against Apache Arrow (only numpy). All integration with arrow is done through Python IIRC. Nice thanks @lithomas1  very cool to see this in!