Allow for none-residue atom entries for protein-ligand graphs

[gcroci2]

• This should allow for atom-level graphs (only for now) to be created.
• Note that the record type HETATM contains coordinates for atoms in nonstandard residues, which include inhibitors, cofactors, ions, and solvent.
  • ATOM + HETATM records

[github-actions]

This issue is stale because it has been open for 30 days with no activity.