perf(stores): defer safeStorage writes off the interaction path (#1941)

* perf(stores): defer safeStorage writes off the interaction path

Session switches funnel every persisted store slice through safeStorage.setItem,
and doing those large JSON.stringify writes synchronously blocked the main
thread for over a second. Add a write-behind buffer that:

- Defers each setItem/removeItem to a later task via setTimeout(0) so the
  click-to-paint path is not blocked.
- Coalesces repeated writes to the same key into a single backing flush.
- Serves pending values from memory so read-after-write stays consistent
  within the deferral window.
- Flushes synchronously on pagehide/beforeunload/visibilitychange/freeze so
  deferred state survives tab close, reload, and the mobile freeze lifecycle.

Adds a test covering write deferral, coalescing, and pending read serving.

* fix(stores): defer persisted JSON serialization

* fix(stores): defer direct safeStorage writes

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/stores/useGitHubPrStatusStore.ts

@@ -1,8 +1,8 @@
 import { create } from 'zustand';
-import { createJSONStorage, persist } from 'zustand/middleware';
+import { persist } from 'zustand/middleware';
 import type { GitHubPullRequestStatus, RuntimeAPIs } from '@/lib/api/types';
 import { mapWithConcurrency } from '@/lib/concurrency';
-import { getSafeStorage } from './utils/safeStorage';
+import { createDeferredSafeJSONStorage } from './utils/safeStorage';
 
 const PR_REVALIDATE_TTL_MS = 90_000;
 const PR_REVALIDATE_INTERVAL_MS = 15_000;
@@ -647,7 +647,7 @@ export const useGitHubPrStatusStore = create<GitHubPrStatusStore>()(
     }),
     {
       name: PR_STATUS_STORAGE_KEY,
-      storage: createJSONStorage(() => getSafeStorage()),
+      storage: createDeferredSafeJSONStorage(),
       partialize: (state) => ({
         entries: Object.fromEntries(
           Object.entries(state.entries)