Provide tool calls in the Client SDK

[JonasHelming]

It would be nice if the client SDK would support tool calls in the sense that I can hand in a function to be called. At the moment, I have to parse the response (in the stream), call the function and then manually send back the result. It would be convenient to avoid this overhead. Other LLM SDKs offer to directly handle tools without manually parsing them.
Maybe I am also overlooking something!