feat: distinguish error and info feedbacks

src/BusProNet/Model/Notification.php

@@ -13,13 +13,8 @@ class Notification
     public ?int $code;
     public ?string $message;
 
-    public function isSuccessful(): bool
+    public function isError(): bool
     {
-        // Successful responses don't carry codes and messages
-        if (null === $this->code && null === $this->message) {
-            return true;
-        }
-
-        return 650 === $this->code && false === stripos($this->message, 'fehler');
+        return 650 !== $this->code;
     }
 }