⏳ Add unit tests

[SusaTyrniluoto]

Pull Request: Add Unit Tests and Improve Core Utility Functions

These changes are implemented in the add-unit-tests branch (previously named improve-link-text-extraction).
All updates are covered with comprehensive unit tests.

Closes

• Closes Improve Deep Merge Function in merge.ts to Handle Primitives, Date Objects, and Circular References #739 – Improve Link Text Extraction with PSL and Punycode Conversion
• Closes ⏳ Add unit tests #740 – Improve Deep Merge Function in merge.ts

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What has been changed

This PR updates two core utility modules (links.ts and merge.ts) and adds thorough unit tests to ensure robust and correct behavior across various edge cases.

links.ts

• Replaces basic domain splitting with the psl (Public Suffix List) library to correctly extract registered domain names.
• Adds support for internationalized domains (IDNs) by decoding Punycode using the punycode library.
• Handles edge cases such as trailing dots in hostnames.
• Improves readability and accuracy of link labels (e.g., https://subdomain.example.co.uk → Example).
• Unit tests added in links.test.ts.

merge.ts

• Rewrites the deep merge logic to correctly handle:
  • Primitive values (e.g., number overwritten by object)
  • Constructed objects (e.g., Date instances preserved with .getTime())
  • Arrays (which are replaced, not merged)
  • Functions (overwritten)
  • Circular references (better error safety)
• Adds full test coverage in merge.test.ts for flat, nested, and edge case scenarios.

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Checklist

• I have reviewed the changes myself in this PR.
• I have added or edited unit tests.
• I have run the unit tests successfully.
• I have run the e2e tests successfully.
• I have tested this change on my own device.
• I have tested this change on other devices (Using Browserstack is recommended).
• I have tested my changes using the WAVE extension
• I have tested my changes using keyboard navigation and screen-reading
• I have added documentation where necessary.
• I have cleaned up the commit history and ensured the commits follow the guidelines