chore(protocol): bump submodule to v1.46.3 and regenerate stubs

Submodule livekit-protocol/protocol: 0bb4e41 -> b89c3a7 (v1.46.3).

Notable additions picked up in the regen:
- agent_session: CustomEvent message + AgentSessionEvent.custom_event
  field (livekit/protocol#1588).
- analytics: FeatureUsageInfo.KRISP_VIVA enum value.
- room: RoomParticipantIdentity.revoke_token_ts field.
- sip: CreateSIPParticipantRequest.{sip_request_uri,sip_to_header,
  sip_from_header} fields.

Generated with protoc 25.1 to match build-protocol.yml.

Author: toubatbrian