fn sniff_insert<T: Timestamp + Lattice>(
diffs: &mut Vec<StateFieldDiff<HollowBatch<T>, ()>>,
upper: &Antichain<T>,
) -> Option<HollowBatch<T>>
fn sniff_insert<T: Timestamp + Lattice>(
diffs: &mut Vec<StateFieldDiff<HollowBatch<T>, ()>>,
upper: &Antichain<T>,
) -> Option<HollowBatch<T>>