修复限流中间件编译错误：移除不存在的GetEntry方法调用，改用滑动窗口限流

AssetManager.API/Middleware/RateLimitMiddleware.cs

@@ -54,14 +54,11 @@ public class RateLimitMiddleware
         }
 
         // 计数+1，首次访问设置过期时间
-        if (requestCount == 0)
+        var cacheEntryOptions = new MemoryCacheEntryOptions
         {
-            _cache.Set(cacheKey, 1, TimeSpan.FromSeconds(WindowSeconds));
-        }
-        else
-        {
-            _cache.Set(cacheKey, requestCount + 1, _cache.GetEntry(cacheKey).AbsoluteExpirationRelativeToNow ?? TimeSpan.FromSeconds(WindowSeconds));
-        }
+            AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(WindowSeconds)
+        };
+        _cache.Set(cacheKey, requestCount + 1, cacheEntryOptions);
 
         await _next(context);
     }