[symfony] Relax RequireRouteNameToGenerateControllerRouteRule for Symfony 6.4+ FQCN routes

[TomasVotruba]

Fixes #326

Since Symfony 6.4, the FQCN route alias is auto-created for any invokable controller that has a #[Route], regardless of its name - see https://symfony.com/blog/new-in-symfony-6-4-fqcn-based-routes

So requiring #[Route(name: self::class)] above __invoke() produced false positives: $router->generate(SomeController::class) resolves fine as long as the controller has any route.

This relaxes the rule to only fire when the __invoke() controller has no #[Route] at all (or has no __invoke()), which is the case where generate() genuinely cannot resolve.

• updated error message and README
• test now asserts an arbitrary route name is accepted; the no-route source fixture is genuinely route-less