Catalog extraction fails on the UK England region's list-valued filter #3922

Problem

On PolicyEngine 6.3.4, catalog extraction fails for the UK:

CatalogExtractionError: region 'country/england' has an unsupported filter value

The England region's scoping strategy now filters on a list of regions (all nine English regions: NORTH_EAST … SOUTH_WEST). _normalize_country in policyengine_api/data/v2/catalog/extraction.py accepted only a scalar variable_value (str, int, float or bool). It refused the list, so the installed-catalog test fails, along with any extraction of the 6.3.4 catalog.

The failure was seen in the "Verify the installed PolicyEngine.py catalog interface" step of the cross-database integration job on #3918.

Expected

Catalog extraction succeeds on 6.3.4. The England region keeps its full membership in the catalog, without a schema change:

• A flat list of scalar values is stored as a JSON array in the existing filter text column.
• Scalar filters keep their current string form.
• Nested, empty, non-finite or over-255-character values are still refused with CatalogExtractionError.