Start building 3.14 wheels

[jaykz52]

This change addresses #65.

It updates the min versions of both nanobind and cibuildwheel to versions that support python 3.14 (and build it by default).

I've also added the skip expression for free-threaded pythons.

[jaykz52]

@leerho @jmalkin tagging you here since I see some recent-ish activity from the both of you on this project. The test suite passes for me locally against python 3.14. Thanks for your time!

[leerho]

• What it does: builds Python 3.14 wheels. It needs nanobind ≥ 2.7 and cibuildwheel ≥ 3.1, and skips free-threaded builds.
• Why it matters now: Python 3.14 has been out for a year. Without wheels, 3.14 users build from source and hit the #71 failure, so today they can't install datasketches at all. Merging #69 and #71 together fixes that.