input: Write a python function to find the top N most common elements in a list using the Counter library.
  assert top_n_elements([1, 3, 5, 3, 6, 2, 4, 6, 8, 4], 5) == [(3, 2), (6, 2), (4, 2), (1, 1), (5, 1)]
  assert top_n_elements([10, 20, 20, 30, 30, 30, 40, 50], 3) == [(30, 3), (20, 2), (10, 1)]
  assert top_n_elements([7, 7, 7, 7, 7, 7, 7], 1) == [(7, 7)]
output: def top_n_elements(lst, n):
      from collections import Counter
      counter = Counter(lst)
      return counter.most_common(n)