input: Write a python function to find all Armstrong numbers in a given range.
  assert find_armstrong_numbers(1, 1000) == [1, 153, 370, 371, 407]
  assert find_armstrong_numbers(100, 999) == [153, 370, 371, 407]
  assert find_armstrong_numbers(1, 500) == [1, 153, 370, 371, 407]
output: def find_armstrong_numbers(start, end):
      def is_armstrong_number(num):
          digits = list(map(int, str(num)))
          power = len(digits)
          return num == sum(d ** power for d in digits)
      
      return [num for num in range(start, end + 1) if is_armstrong_number(num)]