Implement asynchronous save manager with UI update optimizations and add tests for save functionality

world/owniverse/owniverse.gd

@@ -14,6 +14,8 @@ var _group_members: Dictionary = {}
 var _indexed_entity_count: int = -1
 
 var items_to_update: Dictionary[String, float] = {}
+var defer_item_updates: bool = false
+var item_amounts_dirty: bool = true
 
 var auto_production: Array = []
 var locked_entities: Array = []
@@ -146,8 +148,12 @@ func get_item_amounts(total_produced: bool = false) -> Dictionary[String, float]
     return result
 
 
-func refresh_item_amounts() -> void:
+func refresh_item_amounts(force: bool = false) -> void:
+    item_amounts_dirty = true
+    if defer_item_updates and not force:
+        return
     items_to_update = get_item_amounts()
+    item_amounts_dirty = false
 
 
 func _add_time_delta(delta: float) -> Dictionary: