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/components/layout/Navbar.tsx

@@ -23,8 +23,15 @@ export function Navbar() {
   const activeIndex = navLinks.findIndex((link) => link.path === location.pathname);
 
   useEffect(() => {
+    let ticking = false;
     const handleScroll = () => {
-      setIsScrolled(window.scrollY > 20);
+      if (!ticking) {
+        window.requestAnimationFrame(() => {
+          setIsScrolled(window.scrollY > 20);
+          ticking = false;
+        });
+        ticking = true;
+      }
     };
     window.addEventListener('scroll', handleScroll, { passive: true });
     return () => window.removeEventListener('scroll', handleScroll);