Relax numpy<2.4 upper bound for PHEP 3 NumPy 2.4 support #37

Greetings, pyRFU folks, Shawn from PyHC here!

First, thank you again for fixing the previous NumPy 2.0 compatibility issue in pyrfu==2.4.18.

I'm opening this follow-up because pyrfu==2.4.21 currently requires:

numpy>=2.0,<2.4

PyHC's PHEP 3 / SPEC 0-based dependency support policy strongly discourages upper bounds on core scientific Python dependencies unless they are absolutely necessary. The current numpy<2.4 bound is only a warning today, but the PHEP 3 support schedule shows that NumPy 2.4 support becomes required in June 2026. At that point, the PHEP 3 checker will report this upper bound as a compliance error.

This upper bound also contributes to a current PyHC Environment dependency conflict:
heliophysicsPy/pyhc-docker-environment#70

Would you be willing to remove the NumPy upper bound, or relax it enough to allow NumPy 2.4?

If this was originally due to numba==0.63.0 having a numpy<2.4 constraint, newer numba releases appear to allow NumPy 2.4, so one possible path may be to rely on numba's own dependency metadata or raise the minimum numba version if needed.

Thank you!