Generate random stacks for each frame

@jlafleche this is a continuation of Replicator way of doing usd_scene_construction_utils - #7 by Turowicz

The function you helped me with does indeed generate the stacks, but they are the same for each frame of SDG. What I would like is to generate “fresh” stacks for each frame. Unfortunately registering a lambda with the randomizer doesn’t help. My understanding is that I am trying to do something undocumented. That said, it must be possible, since the randomizer.instantiate function does dynamically load and unload USDs. Would you be able to help me with the modification of the code you wrote in the related issue in order to achieve fresh new stacks each frame?

Cheers!