Updated Cosmos3 client to work with vllm-omni server

[MaciejBalaNV]

Description

This PR adds a support for a RoboLab client in vllm-omni. We achieve this by:

1. Added MsgPackWebSocketTransport that handles metadata handshake and auth.
2. Added remote-uri and remote-token - first one is important for choosing the endpoint, second one is important for auth.
3. Correctly parsing the response

Additionally, did some refactoring of the DreamZero model to avoid duplication of the MsgPack code.

On vllm-omni side this PR also needs to be merged: vllm-project/vllm-omni#6460

PR type

• New asset (object / scene / task / robot / variation)
• Bug fix
• New policy backend (policies/<name>/) — requires a paper/project reference and prior contact with the maintainers (see CONTRIBUTING.md)
• Documentation
• Other (describe above)

Checklist

• All commits are signed off (git commit -s) — see DCO
• New Python files carry the standard SPDX header (Apache-2.0, NVIDIA copyright — copy from any existing file)
• New assets are self-contained in their own folder, include their license, and are listed in THIRD_PARTY_NOTICES.md
• Binary files (.usd, meshes, textures, images) are tracked with git-LFS
• uv run pytest tests/ passes locally
• New robots: env configs compile against the benchmark tasks (see docs/robots.md)

Asset attribution