Implement a function deepEqual(a, b) that checks whether two values are deeply equal.

The function should:

• Return true if a and b are equal in value and structure.
• Return false otherwise.
• Handle JSON-serializable values only (numbers, strings, booleans, null, arrays, objects).
• Assume no cyclic references exist.

Examples

deepEqual('foo', 'foo'); // true
deepEqual({ id: 1 }, { id: 1 }); // true
deepEqual([1, 2, 3], [1, 2, 3]); // true
deepEqual([{ id: '1' }], [{ id: '2' }]); // false
deepEqual({ a: [1, { b: 2 }] }, { a: [1, { b: 2 }] }); // true
deepEqual({ a: [1, { b: 2 }] }, { a: [1, { b: 3 }] }); // false