refactor: set content-length as number with outgoing.writeHead()

[yusukebe]

It would be better to use number, even if it may not affect performance.

Content-Length is read in bytes, not characters. Use Buffer.byteLength() to determine the length of the body in bytes. Node.js will check whether Content-Length and the length of the body which has been transmitted are equal or not.

https://github.com/nodejs/node/blob/main/doc/api/http.md#responsewriteheadstatuscode-statusmessage-headers

[yusukebe]

@usualoma

I think it's better, what do you think this?

[usualoma]

@yusukebe
Thank you. I agree!

[yusukebe]

Okay!