Add Clone to graph models, and tests

src/models/frozen_graph.rs

@@ -87,9 +87,16 @@ impl IncidenceCursor<FrozenGraph> for FrozenGraphIncidenceCursor {
 ///
 /// [`degree`] runs in *O(1)* time. Space complexity is *O(|V| + |E|)*.
 ///
+/// # Cloning
+///
+/// [`Vertex`] and [`Edge`] handles obtained from a clone are valid, and refer to the same vertex or
+/// edge in the original, and vice versa. However, once cloned, the two instances no longer affect
+/// each other.
+///
 /// [`degree`]: Self::degree
 /// [`AppendGraph`]: crate::models::AppendGraph
 /// [`Graph`]: crate::models::Graph
+#[derive(Clone)]
 pub struct FrozenGraph {
     vertices: Vec<usize>,
     incidences: Vec<IncidenceEntry>,
@@ -255,6 +262,7 @@ mod trait_tests {
     use super::FrozenGraph;
 
     crate::graph_topology_tests!(FrozenGraph);
+    crate::graph_topology_clone_tests!(FrozenGraph);
 }
 
 #[cfg(test)]