Try to get stuff working

src/Model/Metadata.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pcm\MetadataBundle\Model;
+
+use App\Exception\Dto\Metadata\MissingKeyException;
+use App\Interface\Dto\MetadataInterface;
+
+/**
+ * Store scalar metadata on an entity.
+ */
+final class Metadata implements MetadataInterface
+{
+    /**
+     * @param array<string, scalar|scalar[]> &$metadata
+     */
+    public function __construct(private array &$metadata)
+    {
+    }
+
+    public function get(string $key): mixed
+    {
+        if (!$this->has($key)) {
+            throw new MissingKeyException($key);
+        }
+
+        return $this->metadata[$key];
+    }
+
+    public function set(string $key, mixed $value): static
+    {
+        $this->metadata[$key] = $value;
+
+        return $this;
+    }
+
+    public function has(string $key): bool
+    {
+        return array_key_exists($key, $this->metadata);
+    }
+}
+