Mrinufft

[chaithyagr]

Make pysap-mri compatible with mri-nufft

[chaithyagr]

I have refactored all the codes and now it is ready for review @paquiteau

[paquiteau]

Great job !
Some remarks:

• I think the density examples could be merge into one (to ease the comparison between them).
• You removed the stacked nufft operator, without providing a replacement (there is one in mri-nufft however), maybe we want a dedicated example for that too.

[chaithyagr]

I have now rebased to develop branch to include auto threshold stuff

[chaithyagr]

Great job ! Some remarks:

• I think the density examples could be merge into one (to ease the comparison between them).

While I agree, I kept the CPU and GPU one different fow now to have atleast one on the Gallery. I plan to add cell_count to the SENSE reconstruction stuff . That way we have it all in same place but with a catch that it can be run only on GPU pipeline (self-hosted runner)

• You removed the stacked nufft operator, without providing a replacement (there is one in mri-nufft however), maybe we want a dedicated example for that too.

At the moment I dont see a need for it sadly... We can add one soon when we get to it I guess?