feat: add Node.js 26 support

[ankita10119]

Changes

Adds Node.js 26 to the list of supported engines and CI test matrix.

• package.json engines field updated: ^20.19.0 || ^22.12.0 || ^24.0.0 || ^26.0.0
• .github/workflows/ci.yml test matrix updated: [20.x, 22.x, 24.x, 26.x]

No API, class, or method changes. Node.js 26 is the current active release and users running it with --engine-strict were blocked from installing this package entirely.

References

• Closes Add Node.js 26 support #1355

Testing

Verified locally by running the full test suite on Node.js 26.3.0:

node --version  # v26.3.0                                                                                                                                                 
yarn install --frozen-lockfile
yarn test

Results: 48 test suites, 1643 tests passed, 0 failures.

No new tests were added as this change only extends engine compatibility, no behaviour, APIs, or logic changed.

- This change adds unit test coverage
- This change adds integration test coverage

### Checklist

- [ ] I have read the [Auth0 general contribution guidelines](https://github.com/auth0/open-source-template/blob/master/GENERAL-CONTRIBUTING.md)
- [ ] I have read the [Auth0 Code of Conduct](https://github.com/auth0/open-source-template/blob/master/CODE-OF-CONDUCT.md)
- [ ] All existing and new tests complete without errors

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.62%. Comparing base (57ae86c) to head (861a178).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #1364    +/-   ##
========================================
  Coverage   89.62%   89.62%            
========================================
  Files         428      428            
  Lines       19886    19886            
  Branches     9400     9757   +357     
========================================
  Hits        17823    17823            
  Misses       2063     2063            

Flag	Coverage Δ
alltests	89.62% <ø> (ø)

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