Add a native Cap'n Web adapter for Commands

Add a native Cap'n Web adapter for Commands复制锚点链接

@pluxel/commands/adapters exposes toCapnweb({ method: command }). It creates a native RpcTarget class whose methods execute selected Commands with a trusted constructor context and return JSON data results. The adapter rejects method and data keys that Cap'n Web cannot preserve and checks its encoder before reporting a successful result.