Necessary Maintenance #19884
Create internal implimentation of ParticleList using art::Ptr instead of simb::MCParticle*
The ParticleList is nutools is inconvenient using simb::MCParticle* for storing particles. For purposes of the backtracker/photonbacktracker/particleinventory, it would be beneficial to remove dependence on the ParticleList and build an internal implimentation to do that same, but using art::Ptrs from the event. This will be a beneficial step to moving state for the particle inventory to the event for multithread support.