TEL-912: Return TransferSIPParticipantResponse on TransferSIPParticipantRequests

[genseric-ghiro]

Summary

• Now returning a response for TransferSIPParticipant
• This was previously empty, even though the return type was set to SIPParticipantInfo, which was wrong, and resulted in systematic SIPParticipantInfo(participant_id="", participant_identity="", room_name="", sip_call_id="") responses.

[devin-ai-integration]

✅ Devin Review: No Issues Found

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

[u9g]

The type-check failure here is not from your change. The submodule bump to 17c16cf picks up SimulationRun.List.Request / SimulationRun.Counts.Request, which had a field named from — a Python keyword, so protoc's --pyi_out drops the attribute and falls back to an untyped **kwargs, which this repo's strict mypy rejects. Mine to fix, not yours: livekit/protocol#1738 renames the field. Once that merges, re-bump the submodule and regenerate and the two agent_simulation.pyi errors go away.