chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/sympy/codegen/pynodes.py

@@ -0,0 +1,11 @@
+from .abstract_nodes import List as AbstractList
+from .ast import Token
+
+
+class List(AbstractList):
+    pass
+
+
+class NumExprEvaluate(Token):
+    """represents a call to :class:`numexpr`s :func:`evaluate`"""
+    __slots__ = _fields = ('expr',)