Terminate dynamics early within a SLURM job when it runs out of time

[Alexsp32]

Add a SLURM-aware callback that will terminate a trajectory when the associated SLURM job has less than a threshold time left.

Allow this threshold time to be set manually, in case any output functions that are calculated after termination take particularly long. (e.g. OutputPotentialEnergy)

This could allow us to restart simulations that ran out of time in future.