fix: add regression test for tuple type preservation in snapshot

packages/svelte/tests/types/state.ts

@@ -0,0 +1,15 @@
+import type { ClassValue } from 'svelte/elements';
+
+// Regression test for #17117: this should not trigger deep/infinite type instantiation
+const cls = $state.raw<ClassValue[]>([]);
+const cls_snap: ReturnType<typeof $state.snapshot<ClassValue[]>> =
+	$state.snapshot<ClassValue[]>(cls);
+
+type SnapshotTuple = ReturnType<typeof $state.snapshot<[number, string]>>;
+
+const tuple_ok: SnapshotTuple = [1, 'a'];
+tuple_ok[0] === 1;
+tuple_ok[1] === 'a';
+
+// @ts-expect-error tuple element type should be preserved
+const tuple_wrong: SnapshotTuple = [1, 2];