Update generators::petersen to use graph reserve methods

src/generators.rs

@@ -20,6 +20,8 @@ where
     const N: usize = 5;
     const K: usize = 2;
 
+    graph.reserve_vertices(10);
+    graph.reserve_edges(15);
     let vertices = core::array::from_fn(|_| graph.add_vertex());
     let edges = core::array::from_fn(|j| {
         let i = j / 3;