input: Write a python function to find the closest pair of points from a list of points.
  assert closest_pair([(1,1), (3,3), (-2, 4), (-3, -2), (2, 4)])==((1, 1), (3, 3))
  assert closest_pair([(0, 0), (1, 1), (2, 2), (3, 3)])==((0, 0), (1, 1))
  assert closest_pair([(-1, -1), (-2, -2), (4, 4), (5, 5)])==((-1, -1), (-2, -2))
output: def closest_pair(points):
      import math
      def distance(p1, p2):
          return math.sqrt((p1[0] - p2[0]) ** 2 + (p1[1] - p2[1]) ** 2)
  
      min_distance = float('inf')
      closest_points = (None, None)
      
      for i in range(len(points)):
          for j in range(i + 1, len(points)):
              dist = distance(points[i], points[j])
              if dist < min_distance:
                  min_distance = dist
                  closest_points = (points[i], points[j])
      
      return closest_points