@Override
    default Backoff unwrap() {
        return (Backoff) Unwrappable.super.unwrap();
    }
Undecorates this {@link Backoff} and returns the object being decorated.
If this {@link Backoff} is the innermost object, this method returns itself.

@see Unwrappable
core/src/main/java/com/linecorp/armeria/client/retry/Backoff.java