Unpacks <project>.zip into <project>/ and then deletes the ZIP to free disk space (Bitbucket stops steps that run out of disk). Existing files are not overwritten (unzip -n). If unpacking fails, the ZIP is kept.
After that, if <project>/ contains between one and five ZIP files at its top level, they are unpacked into <project>/ as well, and their names are written to <project>/.zipfile_info as ZIPFILE_SUFFIX for later scripts. ZIP files inside <project>/ are part of the deposit and are never deleted.
--keep-zip - Keep <project>.zip after unpacking. The Download step of 1-populate-from-icpsr uses it, because the ZIP is moved into cache/ for the parallel steps.
project - Deposit directory name. When omitted, it is read from config.yml through tools/resolve_project_id.sh.