Possibly add utils to handle basic WCS in a differentiable way?

[ConnorStoneAstro]

Basic WCS can be composed of a linear transformation (the CD matrix) and simple polynomial distortion perturbations (SIP). These are tedious to implement and may benefit from having utils built into caustics that handle such transformations. These would not be integrated into any particular modules/simulators, but would be available to users in a PyTorch form that is compatible with the rest of caustics. See this paper (and those cited) for a simple description of SIP:
http://tdc-www.harvard.edu/wcstools/SIP_distortion_v1_0.pdf