Refactor subject conversion in AuditEvent2Trail and enhance SubjectConverterInterface

- Replaced `array_map` with `array_reduce` in `AuditEvent2Trail` for flattening converted subjects.
- Enhanced `SubjectConverterInterface` with a `supportsConvert` method and PHPStan annotations to improve type safety and flexibility.

src/Bundle/ChillMainBundle/Audit/AuditEvent2Trail.php

@@ -34,7 +34,13 @@ final readonly class AuditEvent2Trail implements AuditEvent2TrailInterface
             $event->description->trans($this->translator)
             : $event->description;
 
-        $targets = array_map(fn (mixed $subject) => $this->subjectConverterManager->convertEntityToSubjects($subject), $event->subjects);
+        $targets = array_reduce(
+            $event->subjects,
+            function (array $carry, mixed $item): array {
+                return array_merge($carry, $this->subjectConverterManager->convertEntityToSubjects($item));
+            },
+            []
+        );
 
         $user = $this->security->getUser();
 

src/Bundle/ChillMainBundle/Audit/SubjectConverterInterface.php

@@ -11,13 +11,27 @@ declare(strict_types=1);
 
 namespace Chill\MainBundle\Audit;
 
+/**
+ * @template T
+ */
 interface SubjectConverterInterface
 {
     /**
+     * @param T $subject
+     *
      * @return Subject|list<Subject>
      */
     public function convert(mixed $subject): Subject|array;
 
+    /**
+     * Determines whether the given subject is supported for conversion.
+     *
+     * @param mixed $subject the subject to check for conversion support
+     *
+     * @return bool true if the subject can be converted, false otherwise
+     *
+     * @phpstan-assert-if-true T $subject
+     */
     public function supportsConvert(mixed $subject): bool;
 
     public static function getDefaultPriority(): int;