API Gateway v2 HTTP service layer for Rustack.

This crate implements the restJson1 protocol for API Gateway v2, providing:

• Router: Dispatches by HTTP method + URL path
• Handler trait: Defines the boundary between HTTP and business logic
• Service: Hyper Service implementation for the API Gateway v2 protocol
• Response helpers: JSON success/error response formatting

API Gateway v2 uses REST-style routing where each operation has a unique method + path combination. Path parameters (e.g., {apiId}) are extracted and passed to the handler.

Error format

API Gateway v2 errors use a JSON body with a lowercase message field: {"message": "..."}