agent simulation: audio impairments on the create request

[u9g]

Adds background_noise, low_quality_microphone, and packet_loss to SimulationRun.Create.Request, so an audio simulation run can impair the simulated user's audio.

The CLI side is livekit/livekit-cli#943, which turns the --audio flag into an audio subcommand that sends them:

lk agent simulate audio \
  --scenarios scenarios.yaml \
  --background-noise \
  --low-quality-microphone \
  --packet-loss

Nothing consumes the fields yet: agent-service reads only req.GetMode() today, and the simulator will likely need them carried on SimulationDispatch as well.

Overlap worth flagging: the unmerged agent-simulation/scenario-environment-backchannel branch proposes a richer ScenarioGroup.Environment for the same problem space (background_noise as a string, plus audio_events, audio_degradations, backchannel). If that shape is where this is headed, I'm happy to fold these three booleans into it instead.

[changeset-bot]

🦋 Changeset detected

Latest commit: b9d3158

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
github.com/livekit/protocol	Patch
@livekit/protocol	Patch

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