chore: make zod imports tree-shakeable

[MickL]

The following import is not treeshakable:

import { z } from 'zod'

So I replaced it with

import * as z from 'zod'

Further, because zod is not very treeshakable (Issue: colinhacks/zod#2596) and has a huge bundle size, I replaced its first place position in the docs with Valibot which is fully tree shakable, full type safe and has other benifits as well.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@2846

commit: b29cebf

[benjamincanac]

Thanks 😊