perf: throttle scroll event listener in Navbar

Implemented `requestAnimationFrame` throttling for the scroll event listener in `Navbar` to reduce the frequency of state updates and logic execution.

- Wrapped scroll handler in `requestAnimationFrame`.
- Added performance test `src/components/layout/Navbar.test.tsx` verifying logic runs once per frame instead of per event.
- Verified functional correctness of scroll state updates.
- Fixed `useTypingEffect` test environment.

src/hooks/useTypingEffect.test.ts

@@ -1,3 +1,4 @@
+// @vitest-environment jsdom
 import { renderHook, act } from '@testing-library/react';
 import { useTypingEffect } from './useTypingEffect';
 import { describe, it, expect, vi, afterEach, beforeEach } from 'vitest';