Geant4 support in SSD

[fhagemann]

Things that are still needed for full Geant4 support in SSD:

Geometry parsing and GDML file creation

• [ ] Geometry handling of Torus and RegularPrism
• [ ] Correct handling of composite rotations
• [ ] Definition of all compound materials defined in MaterialProperties.jl in the Geant4 materials.xml

Running Geant4 simulations

• [ ] Implement some functions to place a radioactive source and to generate Geant4 events
• [ ] IO for Geant4 simulation output in an SSD compatible format (DetectorHitEvents): see exact format here: https://github.com/JuliaPhysics/SolidStateDetectors.jl/blob/main/src/Units.jl#L102-L113
• [ ] Check that the clustering algorithms in src/ChargeClustering perform well
• [ ] Implement and test functions to generate and save pulse shapes from Geant4 output, maybe even without the need to save the intermediate DetectorHitEvents if not needed

Documentation

• [ ] Documentation on how to use the Geant4 extensions and docstrings for exported/extended functions
• [ ] Tutorial for the documentation (small code example on how to use Geant4 and SSD)