input: Write a function to extract numbers from a given text string using regular expressions.
  assert extract_numbers('I have 2 cats and 3 dogs') == ['2', '3']
  assert extract_numbers('There are 15 apples and 20 oranges') == ['15', '20']
  assert extract_numbers('Room number 101 and 102 are available') == ['101', '102']
output: def extract_numbers(text):
      import re
      return re.findall(r'\d+', text)