simple deallocate function

Author: hjwp

model.py

@@ -21,5 +21,8 @@ def __init__(self, ref: str, sku: str, qty: int, eta: Optional[date]):
     def allocate(self, line: OrderLine):
         self.available_quantity -= line.qty
 
+    def deallocate(self, line: OrderLine):
+        self.available_quantity += line.qty
+
     def can_allocate(self, line: OrderLine) -> bool:
         return self.sku == line.sku and self.available_quantity >= line.qty