Update traits module documentation

src/traits.rs

@@ -1,14 +1,17 @@
+//! Core traits for undirected graph topologies.
+
 use crate::maps::{EdgeMap, VertexMap};
 
 // TODO: Add functions to reserve memory for vertices and edges.
 // TODO: Split out GraphTopologyAddition trait.
+// TODO: Introduce an Incidence struct.
 /// A trait representing an undirected graph topology.
 ///
 /// An undirected graph is a set of vertices and undirected edges, where each edge connects either
 /// exactly two vertices or one vertex with itself (loop edge). This trait provides methods for
 /// querying a graph topology, iterating over vertices and edges, and adding new vertices and edges.
 ///
-/// # Vertices and Edges
+/// # Vertices and edges
 ///
 /// Vertices and edges are identified by opaque handles ([`Vertex`] and [`Edge`]) that implement
 /// [`Copy`] and [`Eq`]. Handles remain valid for the lifetime of the graph unless the graph also