CVE-2026-54911: UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()

ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues.