input: Write a python function to encrypt and decrypt a plaintext using AES encryption.
  assert decrypt(encrypt(b'This is a test.')) == b'This is a test.'
  assert decrypt(encrypt(b'Another test here')) == b'Another test here'
  assert decrypt(encrypt(b'AES encryption test')) == b'AES encryption test'
output: from Crypto.Cipher import AES
  from Crypto.Util.Padding import pad, unpad
  import os
  
  def encrypt(plaintext: bytes) -> bytes:
      key = os.urandom(16)  # 128-bit key
      cipher = AES.new(key, AES.MODE_CBC)
      ciphertext = cipher.encrypt(pad(plaintext, AES.block_size))
      return key + cipher.iv + ciphertext
  
  def decrypt(ciphertext: bytes) -> bytes:
      key = ciphertext[:16]
      iv = ciphertext[16:32]
      encrypted_message = ciphertext[32:]
      cipher = AES.new(key, AES.MODE_CBC, iv)
      plaintext = unpad(cipher.decrypt(encrypted_message), AES.block_size)
      return plaintext