fix(react): ensure that display name is updated upon sign up if requireDisplayName() behaviour is invoked

[russellwheatley]

• onAuthStateChanged now waits for onSignUp call handler to complete so that display name can be updated first.

fixes #1344

Here's React example app with requireDisplayName() behaviour enabled:

Screen.Recording.2026-03-26.at.15.57.36.mov

[gemini-code-assist]

Code Review

This pull request introduces a deduplication mechanism for sign-up events in the SignUpAuthScreen component across both the react and shadcn packages. By utilizing a useRef to track handled user IDs and making the useOnUserAuthenticated hook conditional, the implementation ensures that sign-up callbacks are not triggered redundantly when the form itself handles the success. The changes also include comprehensive test updates to verify the new deduplication logic and hook behavior. Review feedback suggests enhancing type safety in test mocks and maintaining type consistency for the user parameter.