Add Builder interface for improved FunctionCallback construction

[tzolov]

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

[tzolov]

Resolved by #1732