Update market.ts: 是否考虑修改一下插件市场的机制？


如图，用淘宝的npm镜像api 搜索 含有"koishi-plugin-"的npm包
```
https://registry.npmmirror.com/-/v1/search?text=koishi-plugin-&size=50
```

搜索50条，耗时224ms

考虑一下 把这件事情 放在koishi实例本地做？
用来代替现有的插件市场镜像？
或者说 考虑作为一个可选项，实验性功能，可以切换，

Start with market.ts and inspect how the existing plugin-market mirror is queried. Compare that flow with the npm mirror search endpoint described in the issue; the work would need a decided design for local Koishi-instance searching or an optional experimental switch, with the selected behavior working end to end.

Written by the indexing model from the issue text.