Add muon pair production

[amandalund]

This adds the energy distribution, interactor, model, process, and tests for electron-positron pair production by muons.

[github-actions]

Test summary

 3 866 files   5 975 suites   4m 12s ⏱️
 1 605 tests  1 576 ✅ 29 💤 0 ❌
19 858 runs  19 783 ✅ 75 💤 0 ❌

Results for commit f586269.

♻️ This comment has been updated with latest results.

[whokion]

@amandalund Excellent! Just for your information, there is Geant4 TestEm17 example (under extended/electromagnetic) which tests different models of muon processes and can be used for PR verification plots with respect to Geant4 later - of course, our physics validate suite can be used for the model test. Additional observables that can be added are the scattered (post) muon energy (or energy loss) and the angular deviation, which essentially carry equivalent kinematical information for the final state (i.e., distributions of secondaries). Anyway, very nice work!

[amandalund]

Thanks for pointing me to the TestEm17 example @whokion: we still need to validate all of these muon models, and it looks like this will be helpful.

[sethrj]

Looks good! Just a few uses of linterp perhaps, and some documentation updates?

[amandalund]

Thanks for the feedback @sethrj! I think I've addressed everything now.

[sethrj]

@amandalund I think if you merge upstream and re-export the data, we should now have a less preposterous MuPPET size.

[sethrj]

Nice, thanks!

[sethrj]

@amandalund Feel free to merge if you're not waiting on @stognini for feedback.

[stognini]

Sorry for going slowly through the PR, but it looks pretty good to me.

[amandalund]

No prob @stognini, I'll wait until you're through.

[stognini]

Looks great to me. Thanks @amandalund !