fix: auto-fix code issues (cron)

- 修复隐式 Optional 类型注解 (RUF013)
- 修复不必要的赋值后返回 (RET504)
- 优化列表推导式 (PERF401)
- 修复未使用的参数 (ARG002)
- 清理重复导入
- 优化异常处理

backend/rate_limiter.py

@@ -120,7 +120,10 @@ class RateLimiter:
         await counter.add_request()
 
         return RateLimitInfo(
-            allowed=True, remaining=remaining - 1, reset_time=reset_time, retry_after=0,
+            allowed=True,
+            remaining=remaining - 1,
+            reset_time=reset_time,
+            retry_after=0,
         )
 
     async def get_limit_info(self, key: str) -> RateLimitInfo:
@@ -145,9 +148,9 @@ class RateLimiter:
             allowed=current_count < config.requests_per_minute,
             remaining=remaining,
             reset_time=reset_time,
-            retry_after=max(0, config.window_size)
-            if current_count >= config.requests_per_minute
-            else 0,
+            retry_after=(
+                max(0, config.window_size) if current_count >= config.requests_per_minute else 0
+            ),
         )
 
     def reset(self, key: str | None = None) -> None: