CuPy backend

[asmeurer]

We may want to move cupy.array_api to this library as a cupy backend. That would provide support for non-trivial device support, which is currently the one thing that can't really be checked that much through the usage of this library alone.

[leofang]

Q: What's the plan for numpy.array_api? That it'd be moved to this repo starting NumPy 2.0?

cc: @kmaehashi for vis

[asmeurer]

Yes, the plan is to remove it for 2.0.

[lucascolley]

We've just switched from numpy.array_api in SciPy - scipy/scipy#20087