feat(serve-static): support absolute path for root

[yusukebe]

This PR enables the serve static to support an absolute path for the root option.

import { serveStatic } from '@hono/node-server'
import { serve } from '@hono/node-server/serve-static'
import { Hono } from 'hono'

const app = new Hono()
app.use('/static/*', serveStatic({ root: '/home/yusuke/app' }))

serve(app)

Closes #187
Related to honojs/hono#3420

[yusukebe]

Hey @usualoma !

Can you review this?

[yusukebe]

@usualoma

I have some thoughts related to #203 and we don't have to hurry to merge this because this PR may be not needed. So, please don't review this now. Thank you!