chore: use node test runner

[theorderingmachine]

Summary

• remove mocha/chai/c8 and their type packages from devDependencies
• switch unit tests to Node's built-in test runner and coverage
• add lightweight test globals/assertion shims so the existing suite keeps working

Testing

• nix shell nixpkgs#nodejs -c bash -lc "export NODE_ENV=development && npm run test:coverage -- --test-concurrency=1"

Notes

• I ran the test suite locally in a Nix-provided Node environment.
• I did not run npm run lint locally because the repo's vendored Biome binary does not execute under this NixOS environment; CI can validate that path on GitHub.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @theorderingmachine to sign the Salesforce Inc. Contributor License Agreement.

[changeset-bot]

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Latest commit: 506ef11

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[zimeg]

# node:internal/process/esm_loader:40
#       internalBinding('errors').triggerUncaughtException(
#                                 ^
# TypeError [Error]: b.toReversed is not a function or its return value is not iterable

🔬 note: Node 18 tests are failing with some of these changes so we change to the next major version for #2644

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (v5@b942e38). Learn more about missing BASE report.

Additional details and impacted files

@@          Coverage Diff          @@
##             v5    #2854   +/-   ##
=====================================
  Coverage      ?   92.40%           
=====================================
  Files         ?       42           
  Lines         ?     7295           
  Branches      ?      456           
=====================================
  Hits          ?     6741           
  Misses        ?      518           
  Partials      ?       36           

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[WilliamBergamin]

This is awesome 💯

What do you think about holding off on this until we release V5 and merge the branch into the project 🤔 It would only be to keep the changes as targeted as possible to the major release