Complete onboarding exercises

[auleenadas]

Checklist

Please ensure you have followed all of the steps below before submitting a pull request:

• Test your code (npm test or npm run test)
• Check your types (npm run typecheck)
• Lint your code (npm run lint)
• Format your code (npm run format)
• Document your code with TSDoc comments

Overview

Completed the onboarding exercises.

Test Plan

Ran npm run test (all tests passing, including my new tests for mergeSortedNumbers), npm run typecheck (no errors), and npm run lint (no errors) locally before pushing.

[dvorakjt]

Well done. Approved.