feat: add ``getmud`` CLI for UC3 and UC4

[yucongalicechen]

Problem

UCs pasted from #181. Since the functions are already implemented, I think we can include the CLI structure in this release.

UC3: Compute muD from zscan

1. User has a zscan file, and wants to check muD.
2. User uploads zscan file to lpp.gm.
3. lpp.gm returns muD.

UC4: Compute muD theoretically

1. User specifies sample composition, energy, sample mass density, and diameter.
2. User provides this information to lpp.gm.
3. lpp.gm returns muD.

Proposed solution