Scope: Japan e-Gov catalog datasets.
Fetch full metadata for one Japan dataset by its CKAN name or UUID.
Prefer jp_list_resources if you want to see the file list —
that's cleaner. Use this only when you also need description text,
license fields, tags, or created/modified timestamps.
Args:
dataset_id: CKAN name (e.g. "maff_20180521_0148") or id (UUID)