feat(react): create use user mfa service hook and types

[NaveenChand755]

Summary:
Adds useUserMFAService, an internal TanStack Query hook that handles MFA data fetching and mutations (enroll, delete, confirm). Separates the API layer from UI state as the foundation for useUserMFA in the next PR.

Why

The existing MFA implementation bundles data fetching and UI state together, making the API layer hard to test in isolation. This extracts it as a standalone hook.

What

useUserMFAService with factorsQuery, enrollMutation, deleteMutation, confirmEnrollmentMutation
UseUserMFAServiceReturn type + export from hooks/index.ts
10 unit tests

Packages

• packages/core
• packages/react
• examples

References

Testing

How can this be verified? Note anything intentionally not covered by tests and why.

• This change adds unit test coverage
• Tested for both SPA and RWA flows, all example apps working
• All existing and new tests complete without errors

Checklist

• Breaking change
• Requires docs update
• Backward compatible

Contributing

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.47%. Comparing base (7f720a1) to head (8808f44).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #270      +/-   ##
==========================================
+ Coverage   89.42%   89.47%   +0.04%     
==========================================
  Files         159      160       +1     
  Lines       13329    13388      +59     
  Branches     1435     1435              
==========================================
+ Hits        11920    11979      +59     
  Misses       1409     1409              

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