fix: preserve tuple type in `$state.snapshot` (#16864)

* fix: preserve tuple type in `$state.snapshot`

* Update .changeset/lucky-moles-enjoy.md

---------

Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/lucky-moles-enjoy.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve tuple type in `$state.snapshot`

packages/svelte/src/ambient.d.ts

@@ -85,6 +85,8 @@ declare namespace $state {
 			? NonReactive<T>
 			: T extends { toJSON(): infer R }
 				? R
+				: T extends readonly unknown[]
+					? { [K in keyof T]: Snapshot<T[K]> }
 					: T extends Array<infer U>
 						? Array<Snapshot<U>>
 						: T extends object

packages/svelte/types/index.d.ts

@@ -3171,6 +3171,8 @@ declare namespace $state {
 			? NonReactive<T>
 			: T extends { toJSON(): infer R }
 				? R
+				: T extends readonly unknown[]
+					? { [K in keyof T]: Snapshot<T[K]> }
 					: T extends Array<infer U>
 						? Array<Snapshot<U>>
 						: T extends object