fix: stock-snapshots api and service calc wrong result

stock/tests.py

@@ -241,6 +241,7 @@ class CreateStockSnapshotTestCase(StockServicesTestCase):
         self.assertEqual(snapshot.delta, 100)  # 入库数量为正
         self.assertEqual(snapshot.quantity_before, 50)  # 150 - 100
         self.assertEqual(snapshot.quantity_after, 150)
+        self.assertEqual(snapshot.num_of_rolls, self.inventory.num_of_rolls)
         self.assertEqual(snapshot.stock_change_record_id, self.stock_change_in.id)
         
         # 验证日志调用
@@ -257,6 +258,7 @@ class CreateStockSnapshotTestCase(StockServicesTestCase):
         self.assertEqual(snapshot.delta, -50)  # 出库数量为负
         self.assertEqual(snapshot.quantity_before, 200)  # 150 - (-50)
         self.assertEqual(snapshot.quantity_after, 150)
+        self.assertEqual(snapshot.num_of_rolls, self.inventory.num_of_rolls)
     
     def test_create_snapshot_with_invalid_detail(self):
         """测试使用无效明细记录创建快照"""