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/backoff/_jitter.py

@@ -0,0 +1,28 @@
+# coding:utf-8
+
+import random
+
+
+def random_jitter(value: float) -> float:
+    """Jitter the value a random number of milliseconds.
+
+    This adds up to 1 second of additional time to the original value.
+    Prior to backoff version 1.2 this was the default jitter behavior.
+
+    Args:
+        value: The unadulterated backoff value.
+    """
+    return value + random.random()
+
+
+def full_jitter(value: float) -> float:
+    """Jitter the value across the full range (0 to value).
+
+    This corresponds to the "Full Jitter" algorithm specified in the
+    AWS blog's post on the performance of various jitter algorithms.
+    (http://www.awsarchitectureblog.com/2015/03/backoff.html)
+
+    Args:
+        value: The unadulterated backoff value.
+    """
+    return random.uniform(0, value)