Ewald sphere surfaces from atoms

[michael-0brien]

Using jax_finufft.nufft3, it should be straight forward to get ewald sphere surfaces directly from atoms. Using cryojax.experimental.EwaldSphereExtraction and cryojax.simulator.FFTAtomProjection, it should be straightforward to create a class that does this (perhaps named FFTAtomEwaldSphere).

Still need to add tests for EwaldSphereExtraction so that it can be moved out of cryojax.experimental (see #285).