Refactored out claim check logic to its own class

tests/Broker/TopicTest.php

@@ -56,6 +56,7 @@ abstract class _Subscriber implements SubscriberInterface {
     public array $messages = [];
     public function isAuthenticated():bool { return false; }
     public function deliver(Message $message):void { $this->messages[] = $message; }
+    public function getMercureClaims(): ?array { return []; }
     public function getPayload(): ?array { return null; }
     public function getId(): string { return ""; }
 };