Use JSON rather than JSON5 (#2520)
Evaluation so far has shown that agents do a reasonable job of emitting
`json` blocks as arguments when cued (instead of typescript), and `json`
permits the `strict=False` flag to permit control characters, which are
likely to appear in the response in particular.
This PR makes this change to the request and response synthesizer
chains, and fixes the temperature to the OpenAI agent in the eval
notebook. It also adds a `raise_error = False` flag in the notebook to
facilitate debugging
