lights & world: derive Clone for PointLight and World.

rtchallenge/src/lights.rs

@@ -1,6 +1,6 @@
 use crate::tuples::{Color, Tuple};
 
-#[derive(Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct PointLight {
     pub position: Tuple,
     pub intensity: Color,

rtchallenge/src/world.rs

@@ -20,7 +20,7 @@ use crate::{
 /// assert_eq!(w.light, None);
 /// ```
 
-#[derive(Debug, Default)]
+#[derive(Clone, Debug, Default)]
 pub struct World {
     // TODO(wathiede): make this a list of abstract Light traits.
     pub light: Option<PointLight>,