Function stage_object 

fn stage_object(
    descriptor: ObjectDescriptor,
    existing_fingerprints: &BTreeMap<String, String>,
    file_hashes: &BTreeMap<PathBuf, String>,
    variables: &BTreeMap<String, String>,
) -> ObjectPlanStage

Classify a single object as a fingerprint-level Hit or Miss against the stored cache, without loading the cached SQL fragments.