protocol: regenerate agent_simulation for concurrency + SimulationMode

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

Author: theomonnom