Improving integration testing with snapshots

[ataras2]

I've noticed that a few of the tests are only checking if not nan or inf.
I understand that for PSF's etc it can be difficult to hard code test cases, but I think there is a middle ground. Snapshot testing (e.g. https://pypi.org/project/pytest-snapshot/) would allow for the current behavior of the package to be saved in typical scenarios, like a dLux airy disk, and for this to be compared to down the track in case internals like wavefront get changed. This also protects us in the sense that if jax changes the way operations are done (or a Windows install goes wrong #145 ), we get a flag to check things manually.
Thoughts?