Zod 4 supported

[tangye1234]

Is your feature request related to a problem? Please describe.
Currently, server.tool() uses a zod3 raw shape type for its input schema. Zod 4 is now currently release, and our input schema validation is all written in zod 4.

There isn't a compatible conversion between zod 3/4 up to now, so we are stuck here.

Describe the solution you'd like
I recommend to use a custom validation schema as an overload for this method, like vercel/ai-sdk.

Describe alternatives you've considered
We would also like to see the method supports v4/v3 both if the type can be inferred.