feat: use readable stream for the request body

[tangye1234]

Using a ReadableStream instead of buffer.concat provides an improvement in several ways:

1. According to web standards, the request.body should either be null or an instanceof ReadableStream, not Buffer (Uint8Array).
2. In a Hono node server, it's important not to consume the incoming message body until it's actually used.
3. Using a ReadableStream is especially beneficial when clients post large bodies, as it allows the Hono app to be built quickly by the node server.

[tangye1234]

init['body'] = incoming as any

Using this alternative approach might suffice as well. I discovered that @remix-run/web-fetch's Request object can convert a Node.js stream into a ReadableStream through the Stream.on('data', ...) method, which is intended to cater to older versions of Node.js.

However, in terms of the underlying mechanics, it would be more advantageous to use a ReadableStream, given that our Node server is an adapter based on Node 16. Employing async iterators appears acceptable and comes across as more lucid to developers.

[yusukebe]

Hi @tangye1234 !

Great work! I also think it's better to use ReadableStream. Let's go with it!