add caching for inventory searching

src/inventory.ts

@@ -43,12 +43,24 @@ class ItemInstance {
 }
 
 export default class Inventory extends Node {
+  private static cache = new Map()
+
   items: Map<StringName, ItemInstance> = new Map()
 
   static find_inventory(root: Node): Inventory | null | undefined {
+    if (Inventory.cache.has(root)) {
+      return Inventory.cache.get(root)
+    }
+
     const child_enumerator: GArrayEnumerator<Node> = new GArrayEnumerator(root.get_children())
     const children = Enumerable.from(child_enumerator)
-    return children.find(child => child instanceof Inventory) as Inventory
+    const inventory = children.find(child => child instanceof Inventory) as Inventory
+
+    if (inventory != null) {
+      Inventory.cache.set(root, inventory)
+    }
+
+    return inventory
   }
 
   add(item: ItemData, quantity: number = 1) {