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/series/benchmarks/bench_limit.py

@@ -0,0 +1,9 @@
+from sympy.core.numbers import oo
+from sympy.core.symbol import Symbol
+from sympy.series.limits import limit
+
+x = Symbol('x')
+
+
+def timeit_limit_1x():
+    limit(1/x, x, oo)

backend_service/venv/lib/python3.13/site-packages/sympy/series/benchmarks/bench_order.py

@@ -0,0 +1,10 @@
+from sympy.core.add import Add
+from sympy.core.symbol import Symbol
+from sympy.series.order import O
+
+x = Symbol('x')
+l = [x**i for i in range(1000)]
+l.append(O(x**1001))
+
+def timeit_order_1x():
+    Add(*l)