Remove python 3.14 cap

[h-mayorquin]

I think we should remove the <3.14 upper bound on the Python version constraint in pyproject.toml.

The Python version constraint has gone through several iterations:

• PR Cap python 3.13 until we can remove the cap on numpy <2.0 #3480 (Oct 2024): capped at <3.13 due to NumPy 2.0 compatibility issues on Windows and neo dependency problems
• PR Support numpy 2.0 #3640 (Jan 2025): added NumPy 2.0 support with Neo 0.14.0
• PR Test Python 3.13 #3683 (Feb 2025): added Python 3.13 support after fixing MEArec and elephant dependencies

The current <3.14 cap was preemptive and I think a legacy decision of that period when numpy was doing a lot of breaking changes. This is not longer the case.

As discussed in this analysis, Python maintains backward compatibility between minor versions (3.x), so basic code rarely breaks. If our code breaks with a new Python version, it will likely be due to dependency incompatibilities, which will surface at installation time. By removing the cap, we allow these dependency issues to be identified specifically (e.g., "package X doesn't support Python 3.14") rather than being masked by a blanket restriction on SpikeInterface. This helps us identify and fix actual compatibility issues faster.

Related to:
#4173

[chrishalcrow]

Agreed!
Worth noting that "core" spikeinterface works on 3.14 at the moment, but we're artificially not allowing users to use it because numba-based tests fail.