chore: fix phpstan errors, add inline docs

src/Controller/Webhook/MailjetNewsletterWebhookController.php

@@ -51,7 +51,10 @@ final class MailjetNewsletterWebhookController extends AbstractController
     }
 
     /**
-     * @param array<string, mixed> $payload
+     * Mailjet may send one event or a batch of events, so normalize both shapes
+     * into a list before dispatching.
+     *
+     * @param array<int|string, mixed> $payload
      * @return list<array<string, mixed>>
      */
     private function normalizeEvents(array $payload): array
@@ -61,7 +64,14 @@ final class MailjetNewsletterWebhookController extends AbstractController
         }
 
         if (array_is_list($payload)) {
-            return array_values(array_filter($payload, static fn (mixed $entry): bool => is_array($entry)));
+            $events = [];
+            foreach ($payload as $entry) {
+                if (true === is_array($entry)) {
+                    $events[] = $entry;
+                }
+            }
+
+            return $events;
         }
 
         return [$payload];