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/handles/timer.pxd

@@ -0,0 +1,18 @@
+cdef class UVTimer(UVHandle):
+    cdef:
+        method_t callback
+        object ctx
+        bint running
+        uint64_t timeout
+        uint64_t start_t
+
+    cdef _init(self, Loop loop, method_t callback, object ctx,
+               uint64_t timeout)
+
+    cdef stop(self)
+    cdef start(self)
+    cdef get_when(self)
+
+    @staticmethod
+    cdef UVTimer new(Loop loop, method_t callback, object ctx,
+                     uint64_t timeout)