input: Write a python function to encrypt and decrypt a message using a numeric key.
  assert encrypt_message("hello", 3) == "khoor"
  assert decrypt_message("khoor", 3) == "hello"
  assert encrypt_message("world", 5) == "|twqi"
  assert decrypt_message("|twqi", 5) == "world"
output: def encrypt_message(message, key):
      encrypted = ""
      for char in message:
          encrypted += chr(ord(char) + key)
      return encrypted
  
  def decrypt_message(encrypted_message, key):
      decrypted = ""
      for char in encrypted_message:
          decrypted += chr(ord(char) - key)
      return decrypted