Convert to the json schema type that is part of OAS

[CrowdHailer]

I think this saves quite a bit of duplicate work around schema encoding/decoding. let me know if it's useful

I haven't migrated all the tests because the are slightly different field orderings in the output.
Let me know if it's useful to you and I can finish it off

[Neofox]

Hello thanks for your PR.
While I get that it saves some line of code, I am not sure if it's worth adding an additional external dependency for. If the current implementation is limiting, maybe allowing a JSON type instead of a Function type is a better option, this way the user can if he wants use any JSON Schema library he wants as an alternative to generate the tool, the same way it was done with the Structured output.

[CrowdHailer]

Those are fair points.
The reason I want this is because I generate the schema for my tool calls. therefore I don't want to manually write converters to this libraries version of json schema. However if I could still use my generated schemas and pass them in as raw json then everything would also work fine