feat: add router support

[pi0]

Exposing new createRouter utility using unjs/radix3 to create a router.

Usage:

import { createApp, createRouter } from 'h3'

const app = createApp()

const router = createRouter()
 .get('/', () => 'Hello World!')
 .get('/hello/:name', req => `Hello ${req.params.name}!`)

app.use(router)

When using two different methods on the same pattern.