Add to Array-Form of Number

Problem

Given an integer num in array-form (an array of its digits) and an integer k, the function returns the array-form of the result of adding num and k.

The array-form represents the digits of the number from left to right.

The function efficiently handles carrying over digits during addition.

Examples

add([3,4,5,6], 234)
// [3,6,9,0]
// Why? 3456 + 234 = 3690

add([1,9,9], 2)
// [2,0,1]
// Why? 199 + 2 = 201

add([9,9,9], 2)
// [1,0,0,1]
// Why? 999 + 2 = 1001