Set maximum version of the NumPy dependency (NumPy 2.0 is coming)

[evertrol]

I previously wrote:

Aside, something similar should be the case for the NumPy dependency. There should be a minimum version requirement, and a maximum version requirement, for any dependency.

Apparently, I'm slightly clairvoyant, because possibly somewhere end of this year, NumPy 2.0 will be released.

I don't expect the normal API will actually change. But under the hood, a lot might change. And there is some use of NumPy through Cython in XPSI, which may cause unforeseen problems. Patches will likely come for Cython to account for that, but that will be in Cython 3, not 0.29.

So for the moment, you might want to limit the NumPy version to 1.x (~= 1.21 or whatever is a good minimum).

---

Also, spread the word, because this may cause plenty of problems for people trying to install a random half-maintained quick-thrown-together Python package(*) that depends on NumPy. The linked NumPy 2.0 issue/announcement states solutions, but these are for package maintainers, not for innocent users.

(*) I mean one of those many "scientific" Python packages out there that people use in some random project.