input: Write a python function to extract and return all the URLs from a given HTML content using BeautifulSoup and regex.
  assert extract_urls('<html><a href="https://www.example.com">Example Link</a><a href="http://www.example.org">Another Link</a></html>') == ['https://www.example.com', 'http://www.example.org']
  assert extract_urls('<html><a href="https://www.test.com">Test Link</a></html>') == ['https://www.test.com']
  assert extract_urls('<html><a href="http://www.sample.com">Sample Link</a><a href="https://www.another.com">Another Link</a></html>') == ['http://www.sample.com', 'https://www.another.com']
output: def extract_urls(html_content):
      from bs4 import BeautifulSoup
      import re
      
      soup = BeautifulSoup(html_content, 'html.parser')
      urls = []
      
      for link in soup.find_all('a', href=True):
          href = link['href']
          if re.match(r'^https?://', href):
              urls.append(href)
      
      return urls