* In tests, post to `/user/emails/secondary` (6-digits) instead of the deprecated `/user/emails` (link-token)
* Update `addEmailAndConfirm` so it calls the right endpoint
* Remove unnecessary `userId` from `confirmEmail` and `addEmailAndConfirm` args
* Use `updateUser` to add unconfirmed email to user
* Confirm, then unconfirm emails, in order to test on unconfirmed emails
* Lowercase emails in `unconfirmSecondaryEmail`, so they get matched correctly
* Update UserEmailsTests.mjs with 6-digits flow, fetch, no `npm:async`
GitOrigin-RevId: 71b9ed65daebea5f22272240559caab375515f0c
* Rename `sendExistingSecondaryEmailConfirmationCode` to `sendExistingEmailConfirmationCode`
* Deduplicate error handling into `throwIfErrorResponse`
* Update `userHelper.confirmEmail` to use the 6-digits flow
GitOrigin-RevId: 91bdf7b185407b58520ca6b2aa1a7c71bdd23bc8
