input: Write a function to compute the number of words and average word length in a given sentence.
  assert word_count_average_len("hello world") == (2, 5.0)
  assert word_count_average_len("a quick brown fox jumps over the lazy dog") == (9, 3.888888888888889)
  assert word_count_average_len("This is a test sentence.") == (5, 4.2)
output: def word_count_average_len(sentence):
      words = sentence.split()
      word_count = len(words)
      average_length = sum(len(word) for word in words) / word_count if word_count > 0 else 0
      return word_count, average_length