allow getting and setting of recycled entity ids for persistence (#193)

src/Arch/Core/Extensions/Dangerous/DangerousWorldExtensions.cs

@@ -39,6 +39,36 @@ public static void EnsureCapacity(this World world, int capacity)
         world.EntityInfo.EnsureCapacity(capacity);
     }
 
+    /// <summary>
+    /// Gets the recycled entities for the world.
+    /// </summary>
+    /// <param name="world">The <see cref="World"/> instance.</param>
+    /// /// <returns>a tuple (id, version) list of the recycled entities.</returns>
+    public static List<(int, int)> GetRecycledEntityIds(this World world)
+    {
+        List<(int, int)> recycledIdsList = new();
+        foreach (RecycledEntity id in world.RecycledIds)
+        {
+            recycledIdsList.Add((id.Id, id.Version));
+        }
+
+        return recycledIdsList;
+    }
+
+    /// <summary>
+    /// Sets the recycled entities for the world.
+    /// </summary>
+    /// <param name="world">The <see cref="World"/> instance.</param>
+    /// <param name="recycledEntities">A tuple (id, version) list of recycled entites.</param>
+    public static void SetRecycledEntityIds(this World world, List<(int, int)> recycledEntities)
+    {
+        world.RecycledIds.Clear();
+        foreach ((int, int) recycledEntity in recycledEntities)
+        {
+            world.RecycledIds.Enqueue(new RecycledEntity(recycledEntity.Item1, recycledEntity.Item2));
+        }
+    }
+
     /// <summary>
     ///     Sets the <see cref="EntityInfo.Archetype"/> for an <see cref="Entity"/>.
     /// </summary>