Custom iterators must have __next__() and __iter__() defined. Sequence
related iterators in OST only had __next__() defined and this
worked up to Python 3.12. Starting in Python 3.13, list/dict comprehensions
failed.

More info: https://github.com/python/cpython/issues/128161

They are outdated and need substantial updates

restores old behaviour but as far as I can see, this change has no
consequence at all.

Key differences:
 - LigandScorer does not automatically extract non-polymer ligands
   anymore, ligand extraction must happen externally
 - LigandScorer performs cleanup of receptor structure 1) removal of
   hydrogens 2) removal of residues for which there is no entry in
   the PDB component dictionary 3) removal of residues that are not
   peptide linking or nucleotide linking according to PDB component
   dictionary 4) removal of atoms that are not defined for the
   respective entry in the PDB component dictionary.
 - Cleanup is Logged and available as output
 - compare-ligand-structures action does not support automatic
   extraction of ligands from PDB structures anymore. This feature
   still works if structures are provided as mmCIF.
 - compare-ligand-structures action adds receptor structure cleanup
   logs and input parameter in json output to improve
   reproducibility of results.