Cleaned up FillerMask

eco-api/src/main/java/com/willfp/eco/core/gui/slot/FillerMask.java

@@ -54,11 +54,7 @@ public class FillerMask {
     public FillerMask(@NotNull final MaskMaterials materials,
                       @NotNull final String... pattern) {
         this(
-                new MaskItems(
-                        Arrays.stream(materials.materials())
-                                .map(MaterialTestableItem::new)
-                                .toArray(MaterialTestableItem[]::new)
-                ),
+                materials.toMaskItems(),
                 pattern
         );
     }

eco-api/src/main/java/com/willfp/eco/core/gui/slot/MaskMaterials.java

@@ -1,5 +1,6 @@
 package com.willfp.eco.core.gui.slot;
 
+import com.willfp.eco.core.items.Items;
 import org.bukkit.Material;
 import org.jetbrains.annotations.NotNull;
 
@@ -12,5 +13,12 @@ import org.jetbrains.annotations.NotNull;
  */
 @Deprecated(since = "6.24.0")
 public record MaskMaterials(@NotNull Material... materials) {
-
+    /**
+     * Convert MaskMaterials to MaskItems.
+     *
+     * @return The MaskItems.
+     */
+    public MaskItems toMaskItems() {
+        return new MaskItems(Items.fromMaterials(this.materials()));
+    }
 }