feat: unique email addresses of participants unless child, cleanup

addresses #869axbn21

src/BusProNet/Model/Insurance.php

@@ -17,7 +17,7 @@ use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;
 class Insurance
 {
     #[Groups(['api:single', 'api:list'])]
-    public string|null $id = null;
+    public ?string $id = null;
 
     #[Groups(['api:single', 'api:list'])]
     public ?string $code = null;