Add test environment, configuration, and unit tests for utils

[akib22]

Summary

This PR adds a testing environment and initial unit tests for the repository’s utility functions to improve reliability and make it easier for contributors to validate changes.

• Add test configuration and tooling (test framework, setup files, and npm/yarn test scripts).
• Add unit tests for utility functions (cache, fullscreen, utils).

How to run the tests locally

Install dependencies: npm install (or yarn) Run test: npm run test Run test with UI: npm run test:ui Generate coverage: npm run test:coverage

Coverage Report

Request for feedback

• Do you prefer a different testing framework or directory structure for tests?
• I'd appreciate any feedback on the testing strategy and am eager to incorporate your suggestions in upcoming test files

Related to

Issue #635

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