* Add support for ToolOutput response format.
* I don't love the name -- it's confusing unless you know that it's parameterizing a strategy.
We should determine if we want to support our old strategy for doing
things -- it has a higher latency (one extra LLM call), but it's a
reasonable built-in strategy as it doesn't do anything awkward with
conversation history. (Wouldn't surprising if it has overall better
performance than tool choice for longer conversations)
