message: FEAT: Add StableGraph::edge_bound
  New internal feature (will be exposed later)
diff: @@ -735,6 +735,12 @@ impl<N, E, Ty, Ix> StableGraph<N, E, Ty, Ix>
  self.g.raw_edges()
  }
  + fn edge_bound(&self) -> usize {
  + self.edge_references()
  + .next_back()
  + .map_or(0, |edge| edge.id().index() + 1)
  + }
  +
  #[cfg(feature = "serde-1")]
  /// Fix up node and edge links after deserialization
  fn link_edges(&mut self) -> Result<(), NodeIndex<Ix>> {
  