Only raise column-finalisation error for catalogs with unfinalised rows #563
Description
The problem
PR #561 introduced validation that raises a ValueError when a DataRequirement filters or groups on columns declared in columns_requiring_finalisation.
This prevents silent zero-result bugs when those columns contain pd.NA if lazy loading was being used.
The validation currently blocks filtering/grouping on columns_requiring_finalisation unconditionally for any DataCatalog, even when the loaded catalog is already fully finalised (e.g. produced by the "complete" CMIP6 parser where finalised=True and these columns are populated).
This makes those columns effectively unusable with DataCatalog even when they're safe to use.
Definition of "done"
- Handle case if datasets are all finalised