Support multiple tools

[indigoviolet]

Is your feature request related to a problem? Please describe.

Tool use is actually pretty hard to figure out in Instructor because it does something far from the native APIs. Because instructor takes over the tool pathway in the default mode to handle the response model, it requires a custom union-containing type (https://python.useinstructor.com/concepts/unions/?h=union) to support an agent that will return a response model but might also invoke tools (which is a pretty standard pattern).

I'm also concerned that this pattern is not what the models are tuned for, so there might be a slight drop in quality.

Describe the solution you'd like
Instead, I think it should explicitly support a response_model and a list of tool models - and instructor should return a tool model if it was a tool use, or the response model otherwise (perhaps with metadata to distinguish these cases)

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.