Collection routes for a planning table's datasets.

List and the deprecated collection upsert and delete identify a dataset by (table, scenario_id). By-id retrieve, update, delete, and copy live on PlanningTableDatasetDetailViewSet. get_queryset and get_object return the parent PlanningTable.

Consequence for permission_classes: model-derived primitives (ModelPermissions, UserHasModelShared) resolve model_name from the queryset, so they check *_planningtable perms, NOT *_planningtabledataset. Only the hardcoded SpecificModelPermissions / EditSharedPermissions target the dataset model. That is why the expression below mixes table-level and dataset-level permissions.