Write deep_flatten(items) that flattens nested lists of any depth: [1, [2, [3, [4]]], 5] → [1, 2, 3, 4, 5].
deep_flatten([1, [2, [3, [4]]], 5]) → [1, 2, 3, 4, 5]
deep_flatten([]) → []
Submit runs 4 tests, including hidden edge cases.
Run your code to see the output here.