Add GraphTopologyAddition trait from GraphTopology

Move capacity and add methods from GraphTopology trait to new GraphTopologyAddition trait

src/models/graph.rs

@@ -3,7 +3,9 @@
 use typed_generational_arena::{Arena, Index};
 
 use crate::maps::EntityMap;
-use crate::traits::{GraphTopology, GraphTopologyDeletion, Incidence, IncidenceCursor};
+use crate::traits::{
+    GraphTopology, GraphTopologyAddition, GraphTopologyDeletion, Incidence, IncidenceCursor,
+};
 
 /// An opaque handle identifying a vertex in a [`Graph`].
 ///
@@ -239,10 +241,6 @@ impl GraphTopology for Graph {
         self.vertices.len()
     }
 
-    fn vertex_capacity(&self) -> usize {
-        self.vertices.capacity()
-    }
-
     fn vertex_map<T: Clone>(&self, default: T) -> EntityMap<Self::Vertex, T> {
         EntityMap::new(default, |v| v.arr_idx(), self.vertex_capacity())
     }
@@ -251,10 +249,6 @@ impl GraphTopology for Graph {
         self.incidences.len() / 2
     }
 
-    fn edge_capacity(&self) -> usize {
-        self.incidences.capacity() / 2
-    }
-
     fn edge_map<T: Clone>(&self, default: T) -> EntityMap<Self::Edge, T> {
         EntityMap::new(default, |e| e.arr_idx() / 2, self.edge_capacity())
     }
@@ -312,6 +306,16 @@ impl GraphTopology for Graph {
             incidence: self.vertices[v].first_incidence,
         }
     }
+}
+
+impl GraphTopologyAddition for Graph {
+    fn vertex_capacity(&self) -> usize {
+        self.vertices.capacity()
+    }
+
+    fn edge_capacity(&self) -> usize {
+        self.incidences.capacity() / 2
+    }
 
     fn add_vertex(&mut self) -> Self::Vertex {
         self.vertices.insert(VertexIncidenceHeader {