Refactor namespaces from Express\ to Helix- Updated all relevant files to reflect the new namespace structure.

- Adjusted import statements across tests, commands, middleware, and health check classes.
- Ensured consistency in the new Helix namespace throughout the codebase.
- Added a new integration test for Helix to validate application lifecycle and middleware functionality.
- Updated README to reflect changes in the testing framework and integration with HelixPHP

Author: CAFernandes