feat(core): add mfa query keys into core

[NaveenChand755]

Summary
Adds mfaQueryKeys to the core package so TanStack Query cache keys for MFA factors are defined alongside other MFA constants rather than in the React layer.

Why
Query keys are domain constants, not UI concerns. Keeping them in @auth0/universal-components-core next to the MFA factor type constants makes them reusable across any consumer and keeps the React hooks free of hardcoded cache key definitions.

What
Added mfaQueryKeys to packages/core/src/services/my-account/mfa/mfa-constants.ts
Exported mfaQueryKeys from packages/core/src/index.ts

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 89.42%. Comparing base (c1fa8fd) to head (7f720a1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #267   +/-   ##
=======================================
  Coverage   89.42%   89.42%           
=======================================
  Files         159      159           
  Lines       13325    13329    +4     
  Branches     1357     1435   +78     
=======================================
+ Hits        11916    11920    +4     
  Misses       1409     1409           

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