input: Write a python function to find pairs in a list that sum up to a given target.
  assert combination_sums([1, 2, 3, 4, 5], 5) == [[1, 4], [2, 3]]
  assert combination_sums([10, 20, 30, 40, 50], 60) == [[10, 50], [20, 40]]
  assert combination_sums([1, 1, 1, 2, 2], 3) == [[1, 2], [1, 2], [1, 2]]
output: def combination_sums(numbers, target):
      pairs = []
      seen = set()
      for number in numbers:
          complement = target - number
          if complement in seen:
              pairs.append([complement, number])
          seen.add(number)
      return pairs