Route predict output to UUID-named parquet with YAML reference sidecar

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>

pyproject.toml

@@ -10,6 +10,7 @@ dependencies = [
     "pyarrow>=16,<25",
     "tqdm>=4.60,<5",
     "typer>=0.12,<1",
+    "pyyaml>=6,<7",
 ]
 
 [project.optional-dependencies]