input: Write a python function to merge two sorted linked lists into one sorted linked list.
  assert merge_sorted_lists(Node(1), Node(2)).data == 1
  assert merge_sorted_lists(Node(1), Node(2)).next.data == 2
  assert merge_sorted_lists(Node(1), Node(1)).data == 1
  assert merge_sorted_lists(Node(1), Node(1)).next.data == 1
  assert merge_sorted_lists(Node(1), Node(None)) == Node(1)
output: class Node:
      def __init__(self, data):
          self.data = data
          self.next = None
  
  def merge_sorted_lists(l1, l2):
      dummy = Node(0)
      current = dummy
      
      while l1 and l2:
          if l1.data <= l2.data:
              current.next = l1
              l1 = l1.next
          else:
              current.next = l2
              l2 = l2.next
          current = current.next
      
      if l1:
          current.next = l1
      elif l2:
          current.next = l2
      
      return dummy.next