Function build_aggregate_report 

pub fn build_aggregate_report(
    stores: Vec<(String, ImpactStore)>,
    unreadable: usize,
    sort: CrossRepoSort,
) -> CrossRepoImpactReport

Build the cross-repo aggregate from enumerated stores. Excludes enabled-but-empty projects from the rows (counted in project_count), sums totals over every tracked project, and sorts the rows by sort.