Discussion: Compression and Splines

With #604 and #605 compression is being added for ISDs. This issue is to discuss how this might propagate across the stack.

Here are some nominal requirements:
- [ ] Ability to compress/decompress ISDs (done in #604 and #605).
- [ ] Ability to use the compressed ISD straight to memory (no need to decompress to disk).
- [ ] Ability to write an updated compressed ISD to disk after bundle adjustment.
- [ ] Ability to perform adjustment tasks at scale using the CSM. Can one load 1000 ISDs efficiently? 10,000? 100,000?
- [ ] This potentially relates to storing less ephemeris points inside the ISD.
- [ ] An API for consumes of ale to use in their library for working with compressed ISDs.