fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/test_phase7_task6_8.py

@@ -159,7 +159,7 @@ def test_cache_manager() -> None:
 
     # 批量操作
     cache.set_many(
-        {"batch_key_1": "value1", "batch_key_2": "value2", "batch_key_3": "value3"}, ttl=60
+        {"batch_key_1": "value1", "batch_key_2": "value2", "batch_key_3": "value3"}, ttl=60,
     )
     print("   ✓ 批量设置缓存")
 
@@ -208,7 +208,7 @@ def test_task_queue() -> None:
 
     # 提交任务
     task_id = queue.submit(
-        task_type="test_task", payload={"test": "data", "timestamp": time.time()}
+        task_type="test_task", payload={"test": "data", "timestamp": time.time()},
     )
     print("   ✓ 提交任务: {task_id}")
 
@@ -267,7 +267,7 @@ def test_performance_monitor() -> None:
     for type_stat in stats.get("by_type", []):
         print(
             f"   {type_stat['type']}: {type_stat['count']} 次, "
-            f"平均 {type_stat['avg_duration_ms']} ms"
+            f"平均 {type_stat['avg_duration_ms']} ms",
         )
 
     print("\n✓ 性能监控测试完成")