Integrate a LYSO description in ldmx-sw geometry and simulations

[bryngemark]

Is your feature request related to a problem? Please describe. @joyang8caltech has been making standalone Geant4 simulations of a LYSO target geometry, but this won't tell us how a LYSO target would perform in LDMX. We need to pull it into our framework to make studies to scale and with simulations of different types of processes.

Describe the solution you'd like The concrete steps needed are

• [ ] import standalone G4 geometry (from James) into ldmx-sw (see issue https://github.com/LDMX-Software/ldmx-sw/issues/1283 for the 8 GeV version of this)
• [ ] ensure and validate that we can read it out like a TS module
• [ ] set up a procedure for running MadGraph+G4DarkBrem signal generation with LYSO (compound material of other elements than we usually use) (see issue https://github.com/LDMX-Software/ldmx-sw/issues/1228)
• [ ] implement a Birks' law correction for LYSO (see issue #1088)

Consider this a tracking issue. I will make/link to issues for each of these steps.

Describe alternatives you've considered N/A

Additional context Any work in this direction by anyone is welcome. Come to the TS and/or sw dev meetings for help and to showcase your work!