add a from_ref() method to get a Zone from a &Zone

src/world/zone.rs

@@ -17,6 +17,18 @@ pub struct Zone {
 	pub areas: HashSet<Id>,
 }
 
+impl Zone {
+	pub fn from_ref(zone: &Self) -> Self {
+		Self {
+			id: zone.id,
+			parent: zone.parent,
+			name: zone.name.clone(),
+			users_visible: zone.users_visible,
+			areas: zone.areas.clone(),
+		}
+	}
+}
+
 impl Area for Zone {
 	fn id(&self) -> Id {
 		self.id