Feature Request: allow full 3D model rollout visualization

[alberthli]

Feature request from #62.

When visualizing rollouts, show the entire model rolled out along the trajectory with increasing transparency (or some similar visual indicator).

[brentyi]

The next release of Viser will have batched mesh rendering, which may be useful for this: https://github.com/nerfstudio-project/viser/blob/main/examples/01_scene/05_meshes_batched.py

For increasing transparency:

• We could implement a batched_opacities (numpy array with shape (N,)).
• To avoid alpha compositing artifacts, another option is to support per-instance colors. Trajectory could be some kind of gradient / rainbow.

[alberthli]

This would be awesome! Really excited to try it out once things are ready. @pculbertson any additional thoughts on whether you think this would suffice?