Vectorize model

[awohns]

Need to modify the model to support vectorization. So we can do vectorized samples/inference.

See:

    with pyro.plate("particles", 5000, dim=-2):
        guide_trace = poutine.trace(guide_2).get_trace()
        model_trace = poutine.trace(poutine.replay(guide_2.model, guide_trace)).get_trace(
            # TODO model inputs
        )
        loc_sample = model_trace.nodes["internal_location"]["value"]```