Use lenspyx restrict to possibly speed-up lensing #310
Description
Right now, lensing with lenspyx deflects the full-sky and extracts a requested cut-sky. We could instead use the restrict method of lenspyx geometries to possibly speed it up by only performing calculations in the required rings. I'm not sure though and would have to play with it to see how it behaves. This issue is just to track this possible TODO.