Buat count store (writable, awal 5) dan doubled store (derived, count * 2).

Tampilkan: <p>5 x 2 = 10</p>

Hint

• Derived store menghitung nilai dari store lain secara otomatis.
• derived(source, $source => kalkulasi) membuat store turunan.
• const doubled = derived(count, $count => $count * 2);