conftest.py: allow running tests with numpy 2.0

[gabuzi]

Hi,

I thought I'd make the package available on conda-forge so that it can be used itself as a dependency for building other conda packages. See here for the corresponding PR conda-forge/staged-recipes#28200

During building the conda package, I emphasized installability of the package in the conda-forge ecosystem for the tests after the conda package is built, which means I deliberately did not pin the test requirements, which then defaults to installing with numpy 2.x. This revealed the test incompatibility with numpy 2.0 that this PR addresses so that tests can pass with numpy 2.x. It was a simple deprecation of the np.product alias for np.prod, see https://numpy.org/doc/stable/numpy_2_0_migration_guide.html#main-namespace.

An open issue is that by default, the install also with pytorch 2.x, which currently breaks the Toeplitz notebook, but there's already a corresponding issue here #98

Please let me know if you would like to be added as a recipe maintainer for conda-forge, @mmuckley

[mmuckley]

Thanks so much @gabuzi!

You can add me as a maintainer for the conda-forge recipe so that if needed I can apply a patch, but as you can probably tell I'm not spending as much time on torchkbnufft these days so can't guarantee how responsive I'll be :).

With this change maybe we should update the test versions to something a bit more modern for an end-of-year release.

[gabuzi]

Hi @mmuckley

I have added you as a maintainer. It's clear that this is all "best-effort", so no worries about responsivenss – as you say, I think it's just essential to have multiple people in the loop with push access!