refactor(guestbook): move the forms to the new validator
The ruleset becomes typed rule objects injected through ValidatorInterface. NotEmpty disappears from the message and name fields: StringLength requires a value on its own now, which is the same verdict by a shorter route.
Flood and Ban keep the _form key they moved to, and the templates were already reading it.
Flood and Ban keep the _form key they moved to, and the templates were already reading it.