The long-form reader that feeds zone_score_delta(): one row per
(zone, metric) for the zones of fld — Program Areas by default — in one
release's sdm.duckdb. Schema-adaptive like pra_score_delta() (value in
v1–v7, val in v8+) and pinnable to a zone set the same way, so a v6 database
(no zone_set_key column) and a v9 database can be read with one call each
and compared with zone_score_delta().