Compile binary Python wheels for Python 3.12

[janden]

Updates the code to use importlib instead of imp to make the library compatible with Python 3.12. Also updates the wheel building scripts to build wheels for Python 3.12 and test them.

[lu1and10]

@janden Thanks, look great! Just have one question, I saw you committed a dummy extension in cufinufft setup.py and removed that dummy file extension .c file. Does it mean for cufinufft setup.py you don't have this issue commented in the following link?

finufft/python/finufft/setup.py

Line 42 in 1515186

# For certain platforms (e.g. Ubuntu 20.04), we need to create a dummy source

[janden]

I saw you committed a dummy extension in cufinufft setup.py and removed that dummy file extension .c file.

Yes I tried this approach in the other PR (#393) but gave up for now. The reason is that since we include CUDA headers (in order to access the cuFloatComplex and cuDoubleComplex types) in cufinufft.h, we need to make sure those headers are available to Python, which I wanted to avoid. The solution I tried was to convert the CUDA pointers to regular pointers (float complex and double complex in C99 or std::complex<float> and std::complex<double> in C++) but this then meant that I had to perform type casts in other places. So this ended up being a bigger task than I expected. May prepare this in a different PR.

Does it mean for cufinufft setup.py you don't have this issue commented in the following link?

So it does have the same issue. I haven't tried building the wheel on Ubuntu 20.04, but I did encounter it trying to build it on the FI cluster, which from what I understand runs Rocky 8. Installing the binary wheels there should be fine, it's just building them that's problematic due to the linking issue.

At the end of the day, this probably needs a longer discussion in light of #394. Maybe ctypes is not the right fit for us here and we should start considering alternatives.