feat(client): add defaultOptions to createUrlBuilder

[Julien-R44]

createUrlBuilder now accepts an optional third defaultOptions parameter. These defaults (e.g. prefixUrl) are automatically merged into every generated URL, so consumers don't have to repeat them on each call.

Per-call options still take precedence over defaults

const urlFor = createUrlBuilder(routes, stringifier, {
  prefixUrl: 'https://api.example.com'
})

urlFor('users.index') // https://api.example.com/users
urlFor('users.index', undefined, { prefixUrl: '' }) // /users (opt-out)

Also see Julien-R44/tuyau#103 for why its needed

[thetutlage]

Looks good 👍🏽