Add a way for function returns to set options for the next completion

[floomby]

When functions return they create a completion with the existing options from the initial completion. There should be a way to override options in the completion.

What seems like a reasonable approach to me is to have the function return both its results and the option overrides in one object together.

function: async ({ location }) => {
  return {
    value: {
      location: "Albuquerque",
      temperature: "72",
      unit: "fahrenheit",
      forecast: ["sunny", "windy"],
    },
    options: {
      ... options to override here ...
    }
  };
}

This however would be a breaking change. The non breaking, but less ideal seeming, is to pass in a reference to the function and modify the underlying object which is then used for the completion.