Pre-connect final API

[pblazej]

• Implements agent changes: Track vs Room attributes
• Keeps LocalTrack identity while recording/publishing (required by the above ⬆️)
• Adds misc checks for robustness (e.g. don't send to non-agent participants)
• Adds new scoped API for easier cleanup on errors
• Moves "send" part of the stream until the (agent) participant state is ACTIVE to avoid missing stream headers 🤯

[ilo-nanpa]

it seems like you haven't added any nanpa changeset files to this PR.

if this pull request includes changes to code, make sure to add a changeset, by writing a file to .nanpa/<unique-name>.kdl:

minor type="added" "Introduce frobnication algorithm"

refer to the manpage for more information.

[pblazej]

VoiceAssistant PR livekit-examples/agent-starter-swift#16

[pblazej]

To be delivered on the agent side:

• track property check from the proto

[pblazej]

Status quo: let's retest it after moving to SignalClientDelegate + recent bugfixes

[pblazej]

@hiroshihorie feel free to take a look @ the Swift side of things, as there are a couple of moving parts/states here 👍 and I feel like I'm looking at that for too long now 😄

Agents PR: livekit/agents#2171