Function run 

pub fn run(
    spec: &Spec,
    bound: &Bound,
    items: &[Vec<String>],
    facts: Vec<Vec<FactRow>>,
) -> Result<Vec<Row>>

Build the model from the spec, its categories’ items (from items_sql, per category) and its inputs’ rows (from input_sql, per input), evaluate every derived measure, and return one row per derived cell: measures in declaration order, each one’s cells in item order.