feat: add testing framework and initial tests

[thanhhoan-v2]

This pull request introduces a testing framework to the project, addressing the "test code" item noted in the README.md's to-do list.

By setting up Jest and React Testing Library, this provides a foundation for writing unit and component tests, improving code quality and maintainability.

Key Changes:

• Added Dependencies: Installed jest, react-testing-library, ts-jest, and other necessary testing-related packages as development dependencies.
• Jest & TypeScript Configuration:
  • Created jest.config.js to configure Jest to work with TypeScript and a JSDOM environment.
  • Updated tsconfig.json to include the necessary types for Jest and Testing Library.
• Initial Tests: Added an initial test suite for the AnimatedNumbers component in tests/index.test.tsx. These tests verify:
  • The component renders thousand separators correctly.
  • The final digits of the target number are present in the component's output.
• Mocking: Implemented a mock for ResizeObserver to allow the component to render correctly within the JSDOM test environment.
• NPM Script: Added a test script to package.json for easy execution of the test suite.