When no --out is given, predictions are written to a UUID-named parquet
(/ceph central store for ceph inputs, sibling directory otherwise) and a
YAML reference file is created next to the checkpoint recording the output
path, dataset, checkpoint, and timestamp. Adds pyyaml as a core dependency
and unit tests for the two new helper functions.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
