Shutdown immediately if ctrl+c pressed again (#22593)

# Objective

Prevent the program from hanging if user code that runs on shutdown is
buggy.

## Solution

Update the `TerminalCtrlcHandlerPlugin` to exit immediately if `ctrl-c`
is pressed again.

## Testing

I ran this program and verified that it stopped the second time I
pressed `ctrl-c`.
```rust
use bevy::{app::TerminalCtrlCHandlerPlugin, log::LogPlugin, prelude::*};

fn main() {
    App::new()
        .add_plugins((TerminalCtrlCHandlerPlugin, LogPlugin::default()))
        .add_systems(Update, misbehaving_system)
        .run();
}

#[expect(clippy::empty_loop, reason = "testing system that hangs")]
fn misbehaving_system() {
    loop {}
}
```
To automate this it needs to be run in a separate process with a
launcher that kills it if it times out. I'm not sure if that is desired
or how that'd fit into bevy's testing setup.

Author: Person-93

crates/bevy_app/src/terminal_ctrl_c_handler.rs

@@ -1,4 +1,4 @@
-use core::sync::atomic::{AtomicBool, Ordering};
+use core::sync::atomic::{AtomicU8, Ordering};
 
 use bevy_ecs::message::MessageWriter;
 
@@ -7,7 +7,7 @@ use crate::{App, AppExit, Plugin, Update};
 pub use ctrlc;
 
 /// Indicates that all [`App`]'s should exit.
-static SHOULD_EXIT: AtomicBool = AtomicBool::new(false);
+static SHOULD_EXIT: AtomicU8 = AtomicU8::new(0);
 
 /// Gracefully handles `Ctrl+C` by emitting a [`AppExit`] event. This plugin is part of the `DefaultPlugins`.
 ///
@@ -42,17 +42,25 @@ static SHOULD_EXIT: AtomicBool = AtomicBool::new(false);
 pub struct TerminalCtrlCHandlerPlugin;
 
 impl TerminalCtrlCHandlerPlugin {
-    /// Sends the [`AppExit`] event to all apps using this plugin to make them gracefully exit.
+    /// When called the first time, it sends the [`AppExit`] event to all apps using
+    /// this plugin to make them gracefully exit.
+    ///
+    /// If called more than once, it exits immediately.
     pub fn gracefully_exit() {
-        SHOULD_EXIT.store(true, Ordering::Relaxed);
+        if SHOULD_EXIT.fetch_add(1, Ordering::SeqCst) > 0 {
+            log::error!("Received more than one ctrl+c. Skipping graceful shutdown.");
+            std::process::exit(Self::EXIT_CODE.into());
+        };
     }
 
     /// Sends a [`AppExit`] event when the user presses `Ctrl+C` on the terminal.
     pub fn exit_on_flag(mut app_exit_writer: MessageWriter<AppExit>) {
-        if SHOULD_EXIT.load(Ordering::Relaxed) {
-            app_exit_writer.write(AppExit::from_code(130));
+        if SHOULD_EXIT.load(Ordering::Relaxed) > 0 {
+            app_exit_writer.write(AppExit::from_code(Self::EXIT_CODE));
         }
     }
+
+    const EXIT_CODE: u8 = 130;
 }
 
 impl Plugin for TerminalCtrlCHandlerPlugin {