Added performance warning when running stress test examples in debug mode (#5029)

# Objective

Fixes #5028

## Solution
Used #[cfg(debug_assertions)] to display a warning when running examples under stress_tests in debug mode

examples/stress_tests/README.md

@@ -0,0 +1,3 @@
+# Stress tests
+
+These examples are used to stress test Bevy's performance in various ways. These should be run with the --release argument to cargo or equivalent optimization, otherwise they will be very slow.

examples/stress_tests/bevymark.rs

@@ -90,6 +90,8 @@ struct BirdTexture(Handle<Image>);
 struct StatsText;
 
 fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    warn!(include_str!("warning_string.txt"));
+
     let texture = asset_server.load("branding/icon.png");
 
     commands.spawn_bundle(Camera2dBundle::default());

examples/stress_tests/many_cubes.rs

@@ -37,6 +37,8 @@ fn setup(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
+    warn!(include_str!("warning_string.txt"));
+
     const WIDTH: usize = 200;
     const HEIGHT: usize = 200;
     let mesh = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));

examples/stress_tests/many_foxes.rs

@@ -73,6 +73,8 @@ fn setup(
     mut materials: ResMut<Assets<StandardMaterial>>,
     foxes: Res<Foxes>,
 ) {
+    warn!(include_str!("warning_string.txt"));
+
     // Insert a resource with the current scene information
     commands.insert_resource(Animations(vec![
         asset_server.load("models/animated/Fox.glb#Animation2"),

examples/stress_tests/many_lights.rs

@@ -35,6 +35,8 @@ fn setup(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
+    warn!(include_str!("warning_string.txt"));
+
     const LIGHT_RADIUS: f32 = 0.3;
     const LIGHT_INTENSITY: f32 = 5.0;
     const RADIUS: f32 = 50.0;

examples/stress_tests/many_sprites.rs

@@ -33,6 +33,8 @@ fn main() {
 }
 
 fn setup(mut commands: Commands, assets: Res<AssetServer>) {
+    warn!(include_str!("warning_string.txt"));
+
     let mut rng = rand::thread_rng();
 
     let tile_size = Vec2::splat(64.0);

examples/stress_tests/transform_hierarchy.rs

@@ -257,7 +257,10 @@ fn set_translation(translation: &mut Vec3, a: f32) {
 }
 
 fn setup(mut commands: Commands, cfg: Res<Cfg>) {
+    warn!(include_str!("warning_string.txt"));
+
     let mut cam = Camera2dBundle::default();
+
     cam.transform.translation.z = 100.0;
     commands.spawn_bundle(cam);
 

examples/stress_tests/warning_string.txt

@@ -0,0 +1 @@
+This is a stress test used to push Bevy to its limit and debug performance issues. It is not representative of an actual game. It must be run in release mode using --release or it will be very slow.