input: Write a python function to extract comments from an HTML file using BeautifulSoup.
  assert extract_comments('example.html') == ["Comment 1", "Comment 2", "Comment 3"]
  assert extract_comments('comments.html') == ["First comment", "Second comment", "Another comment"]
  assert extract_comments('empty.html') == []
output: def extract_comments(filename):
      from bs4 import BeautifulSoup, Comment
  
      with open(filename, 'r', encoding='utf-8') as file:
          soup = BeautifulSoup(file, 'html.parser')
      
      comments = soup.find_all(string=lambda text: isinstance(text, Comment))
      return [comment.strip() for comment in comments]