feat: Spatius avatar plugin

[3DRX]

Hi LiveKit team! 👋

This PR introduces the Spatius avatar plugin.

Working demos:
👉 Spatius LiveKit Agents Demo
👉 Product home: https://spatius.ai/

User context:
We had 400+ users on SpatialReal platform, and Spatius AI has already picked up 50+ signups in its first few weeks. Around 70% are developers, and most of them are already building on LiveKit — so having the plugin in the main repo would directly help them discover the integration and offer a new affordable live avatar option.
Happy to address any review feedback or run additional tests.

Thanks for your time!

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[3DRX]

@tinalenguyen Hi, sorry for the buzz. I just updated this PR, and resolved all the review and CI checks. It's ready from my point of view, please have a look when you have time :)

Thank you so much for your time.

[3DRX]

To answer questions in #5014

Also, is there a reason why livekit_egress doesn't accept a JWT token instead of LiveKit API secret and key? It would be good to scope credentials to each room that way. I also don't think you need to set audio_output to False in the RoomOptions with that approach

The initial implementation of our LiveKit integration generates livekit token in Spatius' service, which is not good for security. We've changed it since, now the token generation is in this livekit agents plugin.

I tested it out and I wasn't able to see the avatar join the room at all, but audio was published. Could you pull from main and bump the versions to see if that helps?

I've rebased again, pull from main and bump the versions. For my testing it works. https://docs.spatius.ai/livekit-agents/overview Is the documentation we write to help with the setup (a bit more complicated than video streaming avatar, since we do the rendering on client side).