fix: Resolve advanceTimers return type mismatch (Promise<VitestUtils> → Promise<void>)

src/test/harness.ts

@@ -518,7 +518,7 @@ export function createTestHarness(): TestHarness {
     },
 
     // Timer helper - requires vi.useFakeTimers() to be active
-    advanceTimers: () => vi.runAllTimersAsync(),
+    advanceTimers: async () => { await vi.runAllTimersAsync(); },
 
     withFakeTimers: async (fn: () => Promise<void>) => {
       vi.useFakeTimers();