protocol: regenerate agent_simulation for concurrency + SimulationChannel

Bumps the protocol submodule to livekit/protocol#1613 and regenerates the
agent_simulation bindings: SimulationRun.Create.Request.concurrency,
SimulationRun.concurrency, and the SimulationChannel enum (TEXT/AUDIO/SIP)
carried on SimulationDispatch.channel. Also reflects the agent_description
drop from livekit/protocol#1610.

Author: theomonnom