code: def gcs_files(prefix_filter=None):
    
    top_level_xml_str = download_gcs_file("", prefix_filter=prefix_filter)
    xml_root = ElementTree.fromstring(top_level_xml_str)
    filenames = [el[0].text for el in xml_root if el.tag.endswith("Contents")]
    return filenames
docs: List all files in GCS bucket.