load state doesn't update rendering correctly when gpu dynamics is off

[ChengshuLi]

When USE_GPU_DYNAMICS is False and ENABLE_FLATCACHE is False, sometimes load_state will only update the physics, but not the rendering (i.e. physx doesn't update the new object state to USD)

• need to test with ENABLE_FLATCACHE = True
• seem to be unrelated to sleep because even waking up the objects doesn't help

[cgokmen]

I don't know if this is the wake mechanism or not but maybe this logic from PoseAPI can help, you'll at least figure out if it's just a fabric update issue:

            # when flatcache is on
            if og.sim._physx_fabric_interface:
                # no time step is taken here
                og.sim._physx_fabric_interface.update(og.sim.get_physics_dt(), og.sim.current_time)
            # when flatcache is off
            else:
                # no time step is taken here
                og.sim.psi.fetch_results()