[fix #15] ChatFunctionCall arguments field typed as Text

[Saizan]

Here's a fix for issue 15, just changing the type of the field and the To/FromJSON instances.

[agrafix]

Thanks! What if we made this an Either of a parsed value or a text to make it more explicit how it could go "wrong" but keep the benefits of the parsed representation otherwise?

[nickhs]

hey @Saizan, let me know if you'd like to make those changes otherwise happy to do so! I'll also see if I can get a reliable hallucination and add a test

[Saizan]

Feel free to go ahead!