input: Write a function to merge two sorted lists.
  assert MergeTwoLists().merge([1, 3, 5], [2, 4, 6]) == [1, 2, 3, 4, 5, 6]
  assert MergeTwoLists().merge([1, 2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]
  assert MergeTwoLists().merge([1, 2], [3, 4, 5, 6]) == [1, 2, 3, 4, 5, 6]
output: class MergeTwoLists:
      def merge(self, list1, list2):
          merged_list = []
          i, j = 0, 0
          
          while i < list1.length and j < list2.length:
              if list1[i] < list2[j]:
                  merged_list.append(list1[i])
                  i += 1
              else:
                  merged_list.append(list2[j])
                  j += 1
          
          while i < list1.length:
              merged_list.append(list1[i])
              i += 1
          
          while j < list2.length:
              merged_list.append(list2[j])
              j += 1
          
          return merged_list