Replace the removed hashFirmwareFile export with shared stable verifier hashing.
Keep hashing under the file scope and close MCP/file owners independently before
removing their fixture parent. Preserve the primary failure if cleanup also fails.
The actual firmware entrypoint now reaches its prerequisite gate; descriptor
retry and mixed-cleanup controls pass. Real Linux firmware-engine qualification
was not run here. Refs #4912.
morluto
f4456dc196