ZIP central-directory structure

Trap: successful ZipFile.infolist() parsing looks like structural validation because Python accepted the archive, but inconsistent EOCD counts, multi-disk fields, impossible or overlapping offsets, malformed extras, and local/central name disagreement can remain accepted. Fix: validate EOCD, central-directory, and local-header fields from raw bytes and reject every structural inconsistency before trusting member identities or contents.