Fix vertex_capacity and edge_capacity in AppendGraph

Fix AppendGraph::vertex_capacity and AppendGraph::edge_capacity to use the actual capacity of the underlying Vecs.

src/models/append_graph.rs

@@ -93,7 +93,7 @@ impl GraphTopology for AppendGraph {
     }
 
     fn vertex_capacity(&self) -> usize {
-        self.vertices.len()
+        self.vertices.capacity()
     }
 
     fn vertex_map<T: Clone>(&self, default: T) -> VertexMap<Self::Vertex, T> {
@@ -105,7 +105,7 @@ impl GraphTopology for AppendGraph {
     }
 
     fn edge_capacity(&self) -> usize {
-        self.incidences.len() / 2
+        self.incidences.capacity() / 2
     }
 
     fn edge_map<T: Clone>(&self, default: T) -> EdgeMap<Self::Edge, T> {