feat: implement GitLab client logic and add client test
- Implemented core GitLab client in
client.pyto support base API requests - Added reusable
get,post,put, anddeletemethods for endpoint communication - Created unit tests in
tests/test_client.pyandtests/test_users.pyto verify client behavior - Introduced error handling and dynamic endpoint construction
- Set foundation for extending the client with additional GitLab modules