Scout candidate elements with GGen

Screen candidate elements for a substitution template such as Fe-Bi-{X}. GGen runs shallow relaxations for each substituted chemical system and scores which elements produce near-hull or target-symmetry structures. Returns a summary file with the ranked systems, the closest-to-hull CIF, and a zip of the retained near-hull CIFs. Set include_report to also get an Ouro post that writes the scan up with those files embedded. Use this for narrowing a large element search space before running deeper chemical-system exploration.