ISF_Fatras: fix memory leaks in ISF_FatrasToolsG4/G4HadIntProcessor
The use of new in G4HadIntProcessor leads to memory leaks. This is one of the many leaks reported ATLASSIM-5687. This MR replaces the use of new by allocating the relevant objects on the stack and passing them by reference.
These changes only affect simulation with ISF_Fatras.