Function execute_parallel_aggregate_rows 

pub fn execute_parallel_aggregate_rows<'a>(
    input: Box<dyn RowIterator + 'a>,
    group_keys: Vec<TypedExpr>,
    aggregates: Vec<AggregateExpr>,
    having: Option<TypedExpr>,
    final_schema: Vec<ColumnMetadata>,
    parallelism: usize,
) -> Result<Vec<Row>>

Execute a deterministic single-process parallel partial-to-final aggregate.