Add support for all heFFTe MPI communication backends

[rodrigoacb]

This PR extends the available backends available in heFFTe using a enum class to pick the chosen reshape/communication pattern. 

Previously supported: alltoallv and p2p

This adds alltoall and p2p_plined

This changes were done in cooperation with @rhalver

[streeve]

Thanks for the improvements! Do you mind splitting into two PRs? I think I'll want someone else to at least co-review the spline details, but the FFT should be quick to merge

[rodrigoacb]

Thanks for the improvements! Do you mind splitting into two PRs? I think I'll want someone else to at least co-review the spline details, but the FFT should be quick to merge

Hi @streeve Sam! We also thank you for maintaining Cabana! I don't mind splitting the PRs. Should I leave this one for the FFT and create a new one for the Splines?

I had a look into the actions, and I think I have already addressed it with fixes that I can commit once the PRs are at the places.

[streeve]

Thanks for the improvements! Do you mind splitting into two PRs? I think I'll want someone else to at least co-review the spline details, but the FFT should be quick to merge

Hi @streeve Sam! We also thank you for maintaining Cabana! I don't mind splitting the PRs. Should I leave this one for the FFT and create a new one for the Splines?

I had a look into the actions, and I think I have already addressed it with fixes that I can commit once the PRs are at the places.

Yes, that sounds great!

[streeve]

@rodrigoacb sorry for the delay - we will want to rebase this to remove the splines. I'm happy to do that if needed

[rodrigoacb]

Hi @streeve, no problem! Thanks, I will be happy if you can rebase to remove the splines and get the repo to the point it can be merged