Do not cache entities directly in NodesListBuilder but cache only the IDs instead

Otherwise the doctrine proxies break, and we get issues with loading the preview_images in structural Elements.

src/Entity/Attachments/AttachmentContainingDBElement.php

@@ -26,6 +26,7 @@ use App\Entity\Base\AbstractNamedDBElement;
 use App\Entity\Base\MasterAttachmentTrait;
 use App\Entity\Contracts\HasAttachmentsInterface;
 use App\Entity\Contracts\HasMasterAttachmentInterface;
+use App\Repository\AttachmentContainingDBElementRepository;
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
@@ -34,7 +35,7 @@ use Symfony\Component\Serializer\Annotation\Groups;
 /**
  * @template-covariant AT of Attachment
  */
-#[ORM\MappedSuperclass]
+#[ORM\MappedSuperclass(repositoryClass: AttachmentContainingDBElementRepository::class)]
 abstract class AttachmentContainingDBElement extends AbstractNamedDBElement implements HasMasterAttachmentInterface, HasAttachmentsInterface
 {
     use MasterAttachmentTrait;

src/Entity/Base/MasterAttachmentTrait.php

@@ -35,6 +35,8 @@ trait MasterAttachmentTrait
      * @var Attachment|null
      * Mapping is done in the subclasses (e.g. Part), like with the attachments.
      * If this is done here (which is possible in theory), the attachment is not lazy loaded anymore, which causes unnecessary overhead.
+     *
+     * !!! If you change this name, you have to change it in the fetchHint in the AttachmentContainingDBElementRepository (getElementsAndPreviewAttachmentByIDs()) too !!!
      */
     #[Assert\Expression('value == null or value.isPicture()', message: 'part.master_attachment.must_be_picture')]
     protected ?Attachment $master_picture_attachment = null;