Replace cap-async-std

cap-async-std has been removed without a replacement (see https://github.com/bytecodealliance/cap-std/pull/399), because async-std is no longer maintained.
Now there is no way of using async code with this crate.

It would make sense to add either a:
- cap-tokio (I would prefer this one)

or a
- cap-smol

crate to this repository to retain the async functionality of this project.

首先查看 pull request #399 中描述的移除内容，以及仓库中原有的 cap-async-std crate 背景。比较提议的 cap-tokio 和 cap-smol 方向，然后确认替换方案能够在不依赖 async-std 的情况下恢复 async 功能；issue 未指定具体的文件或测试。

由索引模型根据 Issue 内容生成。