Spring-ai Add Builder interface for improved FunctionCallback construction

Problem

The current FunctionCallbackWrapper.Builder implementation has several limitations: - Lacks support for generic type parameters - Builder implementation is tightly coupled with FunctionCallbackWrapper - No standardized interface for different builder implementations - Schema generation is limited to simple class types

Proposed Solution

Introduce a proper FunctionCallback.Builder interface that: - Supports generic type parameters through Spring's ResolvableType - Provides a clean separation between interface and implementation - Enables custom builder implementations while maintaining consistent API - Adds JSON schema generation support for generic types

Comment From: tzolov

Resolved by https://github.com/spring-projects/spring-ai/pull/1732