Cufft primitive

[ASKabalan]

Creating a pure cuda healpix fft to avoid the long compile time when using pure JAX

[matt-graham]

Thanks @ASKabalan for your efforts on this - you've done lots of excellent work here 🎉. I've added some initial high-level comments which are mainly around how this packaged and structured.

The most significant issue at the moment is I think the currently implementation precludes building / installing the package on systems without CUDA which I think we don't want to do - I get a CMake error

      CMake Error at /usr/share/cmake-3.22/Modules/CMakeDetermineCUDACompiler.cmake:179 (message):
        Failed to find nvcc.

        Compiler requires the CUDA toolkit.  Please set the CUDAToolkit_ROOT
        variable.

when trying to pip install the packages with edits here locally in an environment without CUDA.

You've also included some reformatting changes to the s2fft/utils/healpix_ffts.py file which make it difficult to see the more substantive changes you made. Ideally any automatic reformatting should be done in a separate PR to keep the diffs easier to read here and after we've had some discussion about the relevant style guide to follow and formatter to use, so would it be possible for you to revert the formatting changes in that file to make this easier to review.

[ASKabalan]

@matt-graham
I have implemented what you asked

• use nanobind as pip package and not submodule
• remove _src imports when possible
• to be able to compile without cuda (but show error message when the user tries to call cuda functions)

I think that this PR can be merged (if it is all ok for you)
Things we need to take care of

• removing dependency on pyssht if it is failing Issue when import pyssht #206
• formatting Decide on a code style convention and set-up automatic formatting #205

[ASKabalan]

@matt-graham It is ok for me .. go for merge?

[matt-graham]

@matt-graham It is ok for me .. go for merge?

The failing tests are as I forgot we're targetting Python 3.9 and above and I used some Python 3.10 syntax in the type hints. I will fix this now. Then hopefully if tests then pass from my side I'm good to merge, but also tagging @jasonmcewen and @CosmoMatt in case they want to do any final reviews.

[ASKabalan]

@matt-graham Also I think that the test should be marked to not be included in the codecov workflow
Should i do it?

[matt-graham]

@all-contributors please add @ASKabalan for code, review, test

[allcontributors]

@matt-graham

I've put up a pull request to add @ASKabalan! 🎉