Assistant Hook: Add client side function handling and other events

[johannbuscail]

Feature Description

Add events on the useAssistant hook, just like the useChat hook.

https://sdk.vercel.ai/docs/api-reference/use-chat onResponse onError onFinish

But most importantly, making the assistant hook actually useful is the onFunctionCall event. This is a MAJOR and really really important event as it allows the assistant to interact with the client side.

https://sdk.vercel.ai/docs/guides/providers/openai-functions#handling-function-calls-on-the-client

[nico-herrera]

bumping this, need it badly. If anyone has found a solution or workaround please let me know!

[hgrias]

bump