chore: add test for agglomerated `onchange`

packages/svelte/tests/runtime-runes/samples/state-onchange-accumulated/_config.js

@@ -0,0 +1,18 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const [btn, btn2] = target.querySelectorAll('button');
+
+		flushSync(() => {
+			btn.click();
+		});
+		assert.deepEqual(logs, ['foo', 'baz']);
+
+		flushSync(() => {
+			btn2.click();
+		});
+		assert.deepEqual(logs, ['foo', 'baz', 'foo', 'baz']);
+	}
+});

packages/svelte/tests/runtime-runes/samples/state-onchange-accumulated/main.svelte

@@ -0,0 +1,15 @@
+<script>
+	let foo = $state({ bar: 1 }, {
+		onchange(){
+			console.log("foo");
+		}
+	});
+	let baz = $state(foo, {
+		onchange(){
+			console.log("baz");
+		}
+	})
+</script>
+
+<button onclick={()=> foo.bar++}>foo</button>
+<button onclick={()=> baz.bar++}>baz</button>