Apply side effects after running system (#5)

Deferred side effects(Commands) that were pushed in scripting exposed
systems were never applied. This commit applies deferred

assets/examples/side_effects.rhai

@@ -0,0 +1 @@
+spawn_entity();

examples/side_effects.rs

@@ -0,0 +1,51 @@
+use bevy::{app::AppExit, ecs::event::ManualEventReader, prelude::*};
+use bevy_scriptum::{prelude::*, Script};
+
+#[derive(Component)]
+struct Comp;
+
+fn main() {
+    App::new()
+        // This is just needed for headless console app, not needed for a regular bevy game
+        // that uses a winit window
+        .set_runner(move |mut app: App| {
+            let mut app_exit_event_reader = ManualEventReader::<AppExit>::default();
+            loop {
+                if let Some(app_exit_events) = app.world.get_resource_mut::<Events<AppExit>>() {
+                    if app_exit_event_reader
+                        .iter(&app_exit_events)
+                        .last()
+                        .is_some()
+                    {
+                        break;
+                    }
+                }
+                app.update();
+            }
+        })
+        .add_plugins(DefaultPlugins)
+        .add_plugins(ScriptingPlugin::default())
+        .add_systems(Startup, startup)
+        .add_systems(Update, print_entity_names_and_quit)
+        .add_script_function(String::from("spawn_entity"), spawn_entity)
+        .run();
+}
+
+fn spawn_entity(mut commands: Commands) {
+    commands.spawn(Name::new("SpawnedEntity"));
+}
+
+fn startup(mut commands: Commands, assets_server: Res<AssetServer>) {
+    commands.spawn((Script::new(
+        assets_server.load("examples/side_effects.rhai"),
+    ),));
+}
+
+fn print_entity_names_and_quit(query: Query<&Name>, mut exit: EventWriter<AppExit>) {
+    if !query.is_empty() {
+        for e in &query {
+            println!("{}", e);
+        }
+        exit.send(AppExit);
+    }
+}

src/callback.rs

@@ -57,7 +57,9 @@ where
         let mut inner_system = IntoSystem::into_system(self);
         inner_system.initialize(world);
         let system_fn = move |_args: In<Vec<Dynamic>>, world: &mut World| {
-            Dynamic::from(inner_system.run((), world))
+            let result = inner_system.run((), world);
+            inner_system.apply_deferred(world);
+            Dynamic::from(result)
         };
         let system = IntoSystem::into_system(system_fn);
         CallbackSystem {