Implement myFlat(arr, depth = 1)
Write myFlat(arr, depth) that flattens nested arrays up to depth levels deep (default 1, matching Array.prototype.flat).
myFlat([1, [2, 3], [4, [5, 6]]]); // [1, 2, 3, 4, [5, 6]] (depth 1)
myFlat([1, [2, [3, [4]]]], 2); // [1, 2, 3, [4]]
myFlat([1, [2, [3, [4]]]], Infinity); // [1, 2, 3, 4]