Python 3.14 support

[my1e5]

This is a tracking issue for adding support for Python 3.14 which is scheduled for final release on October 7, 2025.

• Upgrade to PyO3 0.26.0 - see https://github.com/PyO3/pyo3/releases/tag/v0.26.0
• Upgrade to numpy 0.26.0 - see https://github.com/PyO3/rust-numpy/releases/tag/v0.26.0

[j824h]

This beautiful library seems to be the only blocker for my environment to move on to Python 3.14.
I hope the migration doesn't take too much effort.

[j824h]

Apparently, merging #85 and then only simply changing the version numbers will work.

[justinjhendrick]

@jvdd, are there more changes to wait for before making the next release? I would like to use tsdownsample on python3.14. Downloading released wheels from PyPI is the most convenient option for my team.