fix: enable to return Response like object

[usualoma]

This PR fixes regression in the #2080.

At first glance, it appears to be a significant change from the following code, but the conditions are the same.

      if (res instanceof Response) return res

      return (async () => {
        let awaited: Response | void
        try {
          awaited = await res
          if (!awaited) {
            return this.notFoundHandler(c)
          }
        } catch (err) {
          return this.handleError(err, c)
        }
        return awaited
      })()

If res instanceof Response is false, whether it is a Promise<Response> or a Response-like object, it is resolved in the subsequent await res. Therefore, it is sufficient to check the type of res with res instanceof Promise and switch its behavior.

Author should do the followings, if applicable

• Add tests
• Run tests
• yarn denoify to generate files for Deno

[yusukebe]

LGTM!

[yusukebe]

This - adding the tests to handle the Proxy object is good!