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/simplify/traversaltools.py

@@ -0,0 +1,15 @@
+from sympy.core.traversal import use as _use
+from sympy.utilities.decorator import deprecated
+
+use = deprecated(
+    """
+    Using use from the sympy.simplify.traversaltools submodule is
+    deprecated.
+
+    Instead, use use from the top-level sympy namespace, like
+
+        sympy.use
+    """,
+    deprecated_since_version="1.10",
+    active_deprecations_target="deprecated-traversal-functions-moved"
+)(_use)