input: Write a function to compress a sequence of integers such that sequences of consecutive elements with the same sign are grouped together.
  assert compress_sequence([9, -2, 6, 0, -7]) == [[9], [-2], [6, 0], [-7]]
  assert compress_sequence([1, 2, 3, -1, -2, -3, 4, 5]) == [[1, 2, 3], [-1, -2, -3], [4, 5]]
  assert compress_sequence([-1, -2, 3, 4, 0, -5, -6]) == [[-1, -2], [3, 4, 0], [-5, -6]]
output: def compress_sequence(seq):
      if not seq:
          return []
  
      compressed = []
      current_group = [seq[0]]
  
      for i in range(1, len(seq)):
          if (seq[i] >= 0 and seq[i-1] >= 0) or (seq[i] < 0 and seq[i-1] < 0):
              current_group.append(seq[i])
          else:
              compressed.append(current_group)
              current_group = [seq[i]]
  
      compressed.append(current_group)
      return compressed