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();