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/uvloop/includes/flowcontrol.pxd

@@ -0,0 +1,23 @@
+# flake8: noqa
+
+
+cdef inline add_flowcontrol_defaults(high, low, int kb):
+    cdef int h, l
+    if high is None:
+        if low is None:
+            h = kb * 1024
+        else:
+            l = low
+            h = 4 * l
+    else:
+        h = high
+    if low is None:
+        l = h // 4
+    else:
+        l = low
+
+    if not h >= l >= 0:
+        raise ValueError('high (%r) must be >= low (%r) must be >= 0' %
+                         (h, l))
+
+    return h, l