Add fetch_profile feature

🔗 Linked Issue

Closes #21

✅ Summary

• Added get_public_profile function to fetch user public profile details from GitLab
• Extended functionality to optionally retrieve native profile README if available
• Implemented unit tests using pytest and requests_mock
• Verified code style with ruff and ensured all tests pass

📋 Checklist

• Lint passed (ruff check .)
• Tests passed (pytest)
• Code is modular & clean
• Proper error handling added for invalid or non-existent usernames