pin Cython to < 3.0

[ChrisBarker-NOAA]

Cython 3.0 is still in beta, but it has quite a few changes, so this should be pinned to less than 3.0 until it can be tested there,

And then it should probably be pinned to >= 3.0

[EpicWink]

Building accelerate with Cython v3.0a11 produces a package which passes the test suite. Up to you whether you want to constrain Cython. In any case, I would avoid the alpha releases of Cython regardless.

[ChrisBarker-NOAA]

Nice!

I agree that building with a pre-release is not a good idea -- I did this 'cause on a project of mine, Cyton 3 breaks a fair bit -- so I didn't think it should be used without testing. The trick is that when 3.0 comes out as a proper release, then builds will automatically start using it.

But if it works with Cython 3, then we probably don't need to constrain.

I'll close this PR.