Feature Request -- (True) Track Lengths

[MeighenBergerS]

During simulations some strange but possible events were identified:

• Events where a single module accounts for >90% of the photon hits (> 40k hits at higher TeV scales.)

These events are theoretically possible but point to an underlying issue. With the current output, it is challenging to identify if these events are genuinely physical or an artifact of the simulation. A way to to benchmark this, would be to identify the track length of the outgoing particles. This would give us an idea of other modules should be seeing the event.

Summary:
Add a new field called "true track length" to the output of the simulation. This should be easy for the water based simulation, since that is a quantity generated by Fennel. Not sure about ice (PPC).