chore(volo-http): use elegant way for creating method router

[wfly1998]

Motivation

The previous way for creating MethodRouter is ugly, this PR updates it with a elegant way.

Previous

# foo is a handler, while Bar is a service

let router = Router::new()
    .route("/", get(foo))
    .route(
        "/index",
        MethodRouter::builder()
            .get(from_handler(foo))
            .post(from_service(Bar))
            .build(),
    )
    .route("/srv", get(from_service(Bar)));

Latest

let router = Router::new()
    .route("/", get(foo))
    .route("/index", get(foo).post_service(Bar))
    .route("/srv", get_service(Bar));

Solution