Function build_halfjoin2 

fn build_halfjoin2<'scope, T, Tr, CF>(
    updates: VecCollection<'scope, T, (Row, Row, T), Diff>,
    trace: Arranged<'scope, Tr>,
    comparison: CF,
    closure: JoinClosure,
    datums: DatumVec,
    errs: VecCollection<'scope, T, DataflowError, Diff>,
) -> (VecCollection<'scope, T, (Row, T), Diff>, VecCollection<'scope, T, DataflowError, Diff>)
where
    T: RenderTimestamp,
    Tr: TraceReader<KeyContainer: BatchContainer<Owned = Row>, Time = T, Diff = Diff> + Clone + 'static,
    for<'a> Tr::Val<'a>: ToDatumIter,
    CF: Fn(Tr::TimeGat<'_>, &T) -> bool + 'static,

half_join2 implementation (less-quadratic, new default).