The Collatz sequence follows a simple rule: if the number is even, divide it by 2; if it is odd, multiply it by 3 and add 1. Write a function collatz_length that repeats this process until the number becomes 1. Return the number of steps needed to reach 1. For n = 1, there are no steps, so the answer is 0.

def collatz_length(n: int) -> int: