examples: migrate async sleep to futures-timer; drop async-std (#19113)

# Objective

- Fixes #19055 

## Solution

- Replace `async-std` with `futures-timer`.

## Testing

CI

---------

Co-authored-by: James Liu <[email protected]>

Author: VitalyAnkh

Cargo.toml

@@ -598,7 +598,7 @@ bevy_image = { path = "crates/bevy_image", version = "0.17.0-dev", default-featu
 bevy_gizmos = { path = "crates/bevy_gizmos", version = "0.17.0-dev", default-features = false }
 # Needed to poll Task examples
 futures-lite = "2.0.1"
-async-std = "1.13"
+futures-timer = { version = "3", features = ["wasm-bindgen", "gloo-timers"] }
 crossbeam-channel = "0.5.0"
 argh = "0.1.12"
 thiserror = "2.0"

examples/async_tasks/async_compute.rs

@@ -6,6 +6,7 @@ use bevy::{
     prelude::*,
     tasks::{block_on, futures_lite::future, AsyncComputeTaskPool, Task},
 };
+use futures_timer::Delay;
 use rand::Rng;
 use std::time::Duration;
 
@@ -62,7 +63,7 @@ fn spawn_tasks(mut commands: Commands) {
                     let duration = Duration::from_secs_f32(rand::rng().random_range(0.05..5.0));
 
                     // Pretend this is a time-intensive function. :)
-                    async_std::task::sleep(duration).await;
+                    Delay::new(duration).await;
 
                     // Such hard work, all done!
                     let transform = Transform::from_xyz(x as f32, y as f32, z as f32);