Use python hide instead of a single-use function

(cherry picked from commit a606fc9ca2)

game/scripts/shops/item/chitchats.rpy

@@ -90,13 +90,8 @@ label purchase_item(item):
         $ game.gold -= item.price
     $ item.owned += 1
 
-    $ item_store_achievements()
-        
-    return
-
-init python:
-    def item_store_achievements():
-        # We require a function because lambdas aren't pickleable
+    python hide:
+        # We hide the lambdas which aren't pickleable
         if isinstance(item, Decoration):
             _posters = filter(lambda x: (x.type == "decoration" and x.placement == poster_OBJ), inventory.items)
             _hats = filter(lambda x: (x.type == "decoration" and "hat" in x.name.lower()), inventory.items)
@@ -105,4 +100,6 @@ init python:
                 achievements.unlock("postman")
 
             if all(i.owned > 0 for i in _hats):
-                achievements.unlock("hats")
+                achievements.unlock("hats")
+
+    return