Refactored code to use PHP8 attributes instead of annotations

In this change, Doctrine and validation annotations have been replaced with PHP8 Attributes. The Rector tool has been configured with a list of annotations to convert to attributes. As a consequence, the PHPStan's rules have been updated to reflect these changes. The PHP8's nullable operator (?) has been added where required, and comments in field declaration have been replaced with #[Attribute] syntax.

src/Bundle/ChillDocStoreBundle/Entity/StoredObject.php

@@ -28,13 +28,10 @@ use Symfony\Component\Serializer\Annotation as Serializer;
  *
  * The property `$deleteAt` allow a deletion of the document after the given date. But this property should
  * be set before the document is actually written by the StoredObjectManager.
- *
- * @AsyncFileExists(
- *     message="The file is not stored properly"
- * )
  */
 #[ORM\Entity]
 #[ORM\Table('chill_doc.stored_object')]
+#[AsyncFileExists(message: 'The file is not stored properly')]
 class StoredObject implements Document, TrackCreationInterface
 {
     use TrackCreationTrait;