int[] arrayMultiplier(int[] arr, int copies)
This method should return an array generated by writing the array arr
several (copies) times in a row.
For example if the array nums = [3, 5, 6]:
arrayMultiplier(nums, 3)
would return the array [3, 5, 6, 3, 5, 6, 3, 5, 6]

int[] multiplied = new int[nums.length * multiplier];