input: Write a python function to find Armstrong numbers up to a given limit.
  assert find_armstrong_numbers(1000) == [0, 1, 153, 370, 371, 407]
  assert find_armstrong_numbers(500) == [0, 1, 153, 370, 371]
  assert find_armstrong_numbers(100) == [0, 1]
output: def find_armstrong_numbers(limit):
      def is_armstrong(n):
          num_str = str(n)
          num_len = len(num_str)
          return n == sum(int(digit) ** num_len for digit in num_str)
      
      return [n for n in range(limit) if is_armstrong(n)]