feat: use Vitest

[LuanRoger]

This pull request includes several significant changes to the testing framework and configuration files. The main changes involve migrating from Jest to Vitest for unit testing, updating configurations, and modifying related documentation.

Migration from Jest to Vitest:

• jest.config.ts and jest.setup.ts: Removed the Jest configuration and setup files as part of the migration to Vitest. [1] [2]
• vitest.config.ts: Added a new Vitest configuration file to set up the testing environment and coverage settings.
• src/tests/unit/ToggleTheme.test.tsx and src/tests/unit/sum.test.ts: Updated test files to use Vitest's test and expect functions. [1] [2]

Updates to configuration files:

• .github/workflows/testing.yml: Renamed the workflow file from playwright.yml to testing.yml, split the test job into tests-unit and test-e2e, and updated the node version to 22.
• package.json: Updated scripts to use Vitest instead of Jest and made minor version updates to some dependencies. [1] [2] [3] [4]

Documentation updates:

• README.md: Updated documentation to reflect the change from Jest to Vitest in the testing sections and directories. [1] [2] [3]