feat(tests): add Vitest configuration and initial test cases

- Introduced a new Vitest configuration file (`vitest.config.ts`) to set up testing environment for the project.
- Added test cases for `exampleActivity` and `exampleWorkflow` functions to ensure expected behavior and correctness.
- Updated `package.json` to include test and coverage scripts using Vitest and c8 for improved testing capabilities.

These changes enhance the testing framework of the project, allowing for better validation of functionality and code quality.

Author: anatolyshipitz