hmc_tm: add real reproducible random numbers mode which will keep the RNG state consistent
across executions of different numbers of trajectories (say you have a serial run doing
1000 trajectories at a time in 10 goes and a parallel run doing 10000 trajectories
in one run, with this mode, the two runs will still have exactly the
same random numbers because the RNG state is saved to file between executions of hmc_tm)