Handle and return all finishreasons

[lalalune]

We should make sure that we're properly handling all the finishreason cases properly in our inner loops and returning the final to the user

Every response will include a finish_reason. The possible values for finish_reason are:
stop: API returned complete message, or a message terminated by one of the stop sequences provided via the stop parameter
length: Incomplete model output due to max_tokens parameter or token limit
function_call: The model decided to call a function
content_filter: Omitted content due to a flag from our content filters
null: API response still in progress or incomplete