input: Write a python function to count the occurrences of a word in a given string, case-insensitively.
  assert count_word_occurrences("Hello, world! This is a sample message.", "hello") == 1
  assert count_word_occurrences("hello hello HELLO", "hello") == 3
  assert count_word_occurrences("No occurrences here", "hello") == 0
output: def count_word_occurrences(s: str, word: str) -> int:
      s_lower = s.lower()
      word_lower = word.lower()
      words = s_lower.split()
      return words.count(word_lower)