ReadonlySavedSaved artifacts, keyed by the returned file id.
Persist the serialized artifact bytes under a name and return the storage file id to record on the model.
the serialized model artifact
a human-readable artifact name (e.g. model-<pipeline>-v<version>.bin)
the file id to store in MLModel.ArtifactFileID
In-memory IArtifactStore for unit tests. Stores bytes in a map keyed by a generated id and returns that id. No database, no MJStorage.