LTX-2 latent preview support

### Feature Idea

Add latent preview to LTX-2 to quickly see if the model goes in a totally wrong direction to interrupt early. It's fast but with better samplers like res_2s it might take a few minutes to even finish the first half-res phase. LTX-2 seems to be the only model that can support it but doesn't: https://github.com/Comfy-Org/ComfyUI/blob/5cd1113236b0fb032a51bf9d63ba196a2510b0d4/comfy/latent_formats.py#L412

### Existing Solutions

Most models, especially video gen, support latent preview. I assume it just needs training a randomly initialized tensor using the model's VAE and various sample media (images/videos). But I couldn't find a working script for that.

### Other

_No response_