Simulation method to request simulation termination

[bemcdonnell]

Looking to add a basic function to terminate a simulation through using a method that requests a simulation to end with the Simulation object. Right now if you want to cleanly end a simulation early you need to exit the iterator within the simulation for loop like this:

with Simulation("model") as sim:
    for ind, step in enumerate(sim):
        if ind == 9:
            break

So if we have a callback set for before_step that could have some basic functionality to end a simulation (like if you are deviating too far out some ideal depth or something).

with Simulation("model") as sim:
    nodeXYZ = Nodes(sim)["nodeZYX"]

    def before_step_callback():
        if nodeXYZ.depth > 8:
            sim.terminate_simulation()

    # Setting Callbacks
    sim.add_before_step(before_step_callback)

    for ind, step in enumerate(sim):
        # Now simulation will end early if the depth is > 8
        pass

Benefits - if you are running optimization it could save you computational time.
Cons - if you like wasting money, you don't get to waste money anymore...