input: Write a python function to calculate the least common multiple (LCM) of a list of numbers.
  assert lcm([2, 4, 6]) == 12
  assert lcm([3, 6, 9]) == 18
  assert lcm([5, 10, 15]) == 30
output: def lcm(numbers):
      from math import gcd
      from functools import reduce
  
      def lcm_two(a, b):
          return a * b // gcd(a, b)
  
      return reduce(lcm_two, numbers)