ENH add InterpolatedImage

[beckermr]

This PR adds interpolated images.

Closes #54

[beckermr]

This PR is blocked on figuring out the differences in this galsim issue: GalSim-developers/GalSim#1248

[beckermr]

Remove this test.

[beckermr]

Blacken

[beckermr]

OK. I figured out the issue here. You need the k-space wrapping and you need to set maxk and stepk to be the same values. Those values for interpolated images in jax-galsim differ a little from galsim and cause rendering differences under convolutions. Once you do this, metacal agrees to better than 1e-7 in absolute tolerance.

[beckermr]

Alright @ismael-mendoza. This PR is a monster, but is ready for review. If you have suggestions on how to break it into smaller chunks, I'd be happy to do that.

[ismael-mendoza]

Thanks! will start taking a look later today and let you know if I have suggestions on how to split it

[ismael-mendoza]

OK @beckermr here is my initial review, still need to review a couple of parts of interpolatedimage.py namely the functions that you had to borrow from C++ code in Galsim

[beckermr]

OK @ismael-mendoza. Back to you!

[ismael-mendoza]

OK almost done, I just don't understand two functions below

[beckermr]

OK @ismael-mendoza ready for one last look!

[ismael-mendoza]

Thanks a lot for the comments @beckermr ! Now it makes sense, just one small comment below and I think it's ready to merge