Implement Clone for everything that can be cloned.

src/geometry/interaction_graph.rs

@@ -10,6 +10,7 @@ pub type TemporaryInteractionIndex = EdgeIndex;
 
 /// A graph where nodes are collision objects and edges are contact or proximity algorithms.
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Clone)]
 pub struct InteractionGraph<T> {
     pub(crate) graph: Graph<ColliderHandle, T>,
 }