Unit testing

[c-dilks]

Is your feature request related to a problem? Please describe.
There is no testing, beyond use cases from elsewhere.

Describe the solution you'd like
Add some unit tests, preferably to the CI (which currently only does a build test).

Describe alternatives you've considered
Try to unit test irt in EICrecon, but that requires knowledge of the geometry or some sample simulation data. To test smaller pieces of the code, it would be better to do some unit testing here.

Note that in the ePIC software stack, we also have reconstruction_benchmarks, which test the full PID (currently just the dRICH).

Additional context
This is motivated by Catch2 testing from EICrecon; since this irt repository is now used in EICrecon, it would be a good idea to do some unit testing here.