Fix z vertex position and add charm information

[tobias-boeckh]

• Fix G4Exceptions: Slow particles can curl in the magnetic field region and get stuck. Added minimum energy requirement of 10 MeV for this region. We still get the hits of all (low-energetic) particles in the upstream pixel detector. This affects only the downstream FASER spectrometer
• Fix vertex z position is fUseFixedZPosition is false: In order to not run GENIE for each geometry (5, 8 mm tungsten, 1 - 3 scintillator layers), I choose a random layer and put the z-position of the neutrino vertex to a random position in the tungsten block in this layer. If we have two tugnsten blocks, due to the scintillators, I also chose one of them randomly.
• Added the PDG ids of more charmed hadrons to the Py8DecayerPhysics
• Added a hit_fromCharmedHadron variable to the pixel hits to tag charm charm neutrino interactions (nu->X+c)