Function find_blocking_flow 

fn find_blocking_flow<G>(
    network: G,
    source: G::NodeId,
    destination: G::NodeId,
    flows: &mut [G::EdgeWeight],
    level_edges: &mut [Vec<G::EdgeRef>],
    visited: &mut G::Map,
) -> G::EdgeWeight
where
    G: NodeCount + IntoEdges + NodeIndexable + EdgeIndexable + Visitable,
    G::EdgeWeight: Sub<Output = G::EdgeWeight> + PositiveMeasure,

Find blocking flow for current level graph by repeatingly finding augmenting paths in it.

Attach computed flows to flows and returns the total flow increase from edges available in level_edges at this iteration.