ENH add photon shooting

[beckermr]

This PR is another monster. I am happy to break it up for folks if needed. The main reason it got so big is that I wanted to ensure enough tests were running that I flushed out all of the bugs. There were quite a few in fact.

Main features:

• I added implementations for PhotonArray, Sensors, and associated photon shooting methods on GSObjects
• I removed test routines copied from galsim in favor of pointing to the galsim test suite with changes as needed. This change will make it easier to sync the code in those routines with the upstream galsim ones as galsim APIs change.
• I refactored how the random number generators work so that state can be carried everywhere except across JIT boundaries.
• I added specialized interfaces for photon shooting with fixed-size arrays. This makes those methods JIT compatible. The initial performance tests are better than expected.
• I refactored a bit of the test suite to ensure nothing was removed since we had some custom tests with the galsim ones we had copied.

To do:

• [x] add PhotonArrays
• [x] enable shooting for GSObjects
• [x] enable tests from galsim
• [x] add tests of RNG handling to make sure seed and state are propagated correctly
• [x] add comments to dense code
• [x] add API tests for PhotonArray
• [x] add API tests for Sensors
• [x] add tests of fixed-size photon array and mask handling

[beckermr]

This PR is ready for review. I expect it to take a while since it is so big. If you'd like it broken up, feel free to suggest ways to do so.

[ismael-mendoza]

Hi @beckermr - just an update. I'm making good progress with the review and should be finished in the next couple of days

[beckermr]

OK @ismael-mendoza. Back to you!