Numpy 2 support

[sapols]

PlasmaPy intends to support numpy >= 2.0.0 in their next release, but I don't believe other core packages will be so quick to adopt it.

So for now, let's manually pin that upper bound.

[sapols]

We're no longer getting the latest version of sunpy because 6.0.0 requires numpy>=2 while we're still requiring numpy<2.

[jtniehof]

numpy 2.0 has worked with SpacePy since at least 0.6.0 (I think 0.5.0 too), but 0.7.0 removes all build issues and some deprecations.

[namurphy]

⚠️ Packages that follow the dependency support window in SPEC 0 will start requiring numpy>=2.0 around mid-September 2025, so it's going to be important for packages in the heliopythoniverse to have numpy>=2.0 support soon.