Make killbox kind also an export

rust/src/killbox.rs

@@ -10,7 +10,7 @@ use crate::{
     player::{DamageSource, IPlayer, ball::Ball},
 };
 
-#[derive(Debug, Clone, Copy, GodotConvert, Default, Var, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, GodotConvert, Default, Var, Serialize, Deserialize, Export)]
 #[godot(via = GString)]
 pub enum KillboxKind {
     #[default]
@@ -49,6 +49,7 @@ impl KillboxKind {
 #[derive(GodotClass)]
 #[class(base=Area3D, init)]
 pub struct Killbox {
+    #[export]
     #[var]
     pub kind: KillboxKind,