Isotope bug fixes and tests

We need C isotopes to work in CESM3, so I'm going to group these card here for clarity. There's enough here that I wonder if we need to assign this to someone and prioritize the work and will create an issue to bring it up at an upcoming SE meeting.

- [ ] https://github.com/ESCOMP/CTSM/issues/3350
- [ ] https://github.com/ESCOMP/CTSM/issues/1358
- [ ] https://github.com/ESCOMP/CTSM/issues/592
- [ ] https://github.com/ESCOMP/CTSM/issues/231
- [ ] https://github.com/ESCOMP/CTSM/issues/182
- [ ] https://github.com/ESCOMP/CTSM/issues/181
- [ ] https://github.com/ESCOMP/CTSM/issues/67
- [ ] https://github.com/ESCOMP/CTSM/issues/44

NOTE: We want to make sure the model aborts when you are trying to run isotopes from a finidat file without it (should be one of the above issues). We will also need to create a set of finidat files when CTSM5.2 comes in.