Use Futures instead of latches to synchronize request processing

* Framework version: 2.0
* Implementations: All

## Scenario
The framework currently uses latches on the `HttpServletResponse` implementation to wait for the completion of a request. We should change this to use Futures. This need for this was highlighted in #272 as throwing an exception without releasing the latch may cause memory leaks.

首先追蹤 HttpServletResponse 的實作以及請求處理期間所使用的 latch 生命週期，然後檢視 issue #272，了解可能導致 latch 未釋放的例外路徑。完成的標準是：所有實作中的請求完成都使用 Futures 而不是 latches，並且在發生例外時不會保留資源。

由索引模型根據 Issue 內容生成。