feat: restructure project to follow standard layout and integrate uv with CI. Linked to issue #22

This Merge Request modernizes the gitlab-wrapper repository structure and tooling for maintainability and compatibility with modern Python packaging and CI standards:

♻️ Refactored project layout to src/ structure (src/gitlab_wrapper/)

🛠️ Added pyproject.toml with PEP 621 metadata, optional dev dependencies, and setuptools configuration

⚡ Integrated uv as the default package and virtual environment manager for faster, deterministic installs

🔧 Updated .gitlab-ci.yml to use uv instead of pip/venv for CI/CD consistency

🧪 Ensured pytest and ruff are installed and configured for testing and linting

📦 Updated .gitignore to exclude .venv/ and uv.lock

This aligns with the standard project structure expected by Python tooling and improves setup reproducibility for developers and CI systems.