MAINT: add Python 3.14, drop 3.9, fix some CI and build stuff

[rgommers]

Python 3.14 is in the release candidate stage, meaning this is the time to add 3.14 wheels on PyPI.

Changes:

• Add Python 3.14
• Drop Python 3.9, it's end of life (I considered dropping 3.10 as well, because NumPy already did - but decided against that since it costs little to keep it)
• Fix CI for GHA dropping windows-2019
• Add free-threading trove classifier
• Bump numpy upper bound up

Also, two questions @rdbisme:

• Any preference for making the next release number 1.6.0 vs 1.5.1? Either way should work; I'd lean towards 1.6.0 because of dropping Python 3.9
• Support for Intel Macs will disappear on GHA starting 1 Sep: https://github.blog/changelog/2025-07-11-upcoming-changes-to-macos-hosted-runners-macos-latest-migration-and-xcode-support-policy-updates/#macos-13-is-closing-down. Are you okay with just dropping those wheels, probably after doing one more release with it now? Seems like the easiest, and I expect that that is what many projects will do.

EDIT: see this CI log for a full set of (passing) wheel builds.

[rdbisme]

Any preference for making the next release number 1.6.0 vs 1.5.1? Either way should work; I'd lean towards 1.6.0 because of dropping Python 3.9

Yes, 1.6.0 sounds good to me

Support for Intel Macs will disappear on GHA starting 1 Sep: https://github.blog/changelog/2025-07-11-upcoming-changes-to-macos-hosted-runners-macos-latest-migration-and-xcode-support-policy-updates/#macos-13-is-closing-down. Are you okay with just dropping those wheels, probably after doing one more release with it now? Seems like the easiest, and I expect that that is what many projects will do.

I definitely trust your judgment here, you have way more experience with this. I was a user of macports, which tries to keep things going for old macs, but not having infrastructure to compile it on makes it difficult. I guess it's impossible to crosscompile on Mac Arm?

[rdbisme]

cibuildwheel: Invalid skip selector: 'pp*'. This selector matches a group that wasn't enabled. Enable it using the enable option or remove this selector. This selector will have no effect.

Apparently that skip selector is not needed anymore with new cibuildwheel?

[rgommers]

but not having infrastructure to compile it on makes it difficult. I guess it's impossible to crosscompile on Mac Arm?

The cross compile part is easy, but shipping binaries without ever running the tests for that build setup feels quite uncomfortable. I'd personally much prefer not to do that. And support across packages will become spotty fairly quickly anyway, so my sense is that soon enough the reliable way to install a set of packages will be to base it on the cutoff date where GitHub support disappeared with https://docs.astral.sh/uv/reference/settings/#exclude-newer

Apparently that skip selector is not needed anymore with new cibuildwheel?

Ah yes, right, cibuildwheel 3.0 changed what is selected by default. I'll clean up this warning in a follow-up.