Refactor Registry & RegistryBackend API

[JeremyWurbs]

Description

Refactor the RegistryBackend API to do the following:

1. Support batch operations;
2. Move all locking operations to be internal to each backend;
3. Remove overwrite as part of the public API;

Explicitly, the RegistryBackend API should be:

# Objects API
push(self, name: str | list[str], version: str | list[str], local_path: str | Path | list[str | Path], metadata: dict | list[dict] | None = None)
pull(self, name: str | list[str], version: str | list[str], local_path: str | Path | list[str | Path])
delete(self, name: str | list[str], version: str | list[str])

# Object Metadata API
save_metadata(self, name: str | list[str], version: str | list[str], metadata: dict | list[dict])
fetch_metadata(self, name: str | list[str], version: str | list[str]) -> dict[str, dict]
delete_metadata(self, name: str | list[str], version: str | list[str])

# Serialization
register_materializer(self, object_class: str | list[str], materializer_class: str | list[str])
registered_materializers(self, object_class: str | None | list[str]) -> dict[str, str]

# Registry-level Metadata
save_registry_metadata(self, metadata: dict)
fetch_registry_metadata(self) -> dict

# Discovery
list_objects(self) -> list[str]
list_versions(self, name: str | list[str]) -> dict[str, list[str]]
has_object(self, name: str | list[str], version: str | list[str]) -> dict[str, bool]

# Utility Methods
validate_object_name(self, name: str | list[str]) -> None  # raise exception if any names fail

The associated Registry methods should also support batch operations:

save(self,
    name: str | list[str],
    obj: Any | list[Any],
    *,
    materializer: Type[BaseMaterializer] | None | list[Type[BaseMaterializer]] | list[None] = None,
    version: str | list[str] | None = None,
    init_params: Dict[str, Any] | None | list[Dict[str, Any] | None] = None,
    metadata: Dict[str, Any] | None | list[Dict[str, Any] | None] = None,
)

# similarly for load, delete, info, etc.

Acceptance Criteria

• Complete Registry implementation
• Complete support for the three main backends: Local, Minio and GCP
• 100% unit test coverage
• Expanded integration test suite

Priority

High (blocking release or critical path)

Estimated Effort (Story Points)

8 (1 week or more)