Feature Request: support multiple app responses in multi-turn simulator

Hi!
I've created an Agent with LangGraph that can sometimes respond with multiple messages, and I'd love to use the `runMultiturnSimulation` util with it, but it looks like right now the simulator only supports returning a single message :/

For now I've wrapped the agent in a function that collapses the messages into a single one, but it would be nice to see this supported out of the box!