implement the basic version of DES by python

• read_key(key_file: str) -> bytes: Reads a key from a file and returns it as bytes.
• save_key(key_file: str, key: bytes): Saves a key to a file.
• generate_key(key_len=256) -> bytes: Generates a random key of the specified length in bits and returns it as bytes.

• bitize(byts: bytes) -> list[int]: Converts bytes into a list of bits.
• debitize(bits: Iterable[int]) -> bytes: Converts a list of bits into bytes.
• bit2hex(bits: Iterable[int]) -> str: Converts bits into a hexadecimal string.
• hex2bit(hex_str: str) -> list[int]: Converts a hexadecimal string into bits.

• key_generation(key: list[int]) -> list[list[int]]: Generates 16 round subkeys from the initial 64-bit key.

• enc_block(block: list[int]) -> list[int]: Encrypts a 64-bit block using DES.
• mixer(L: list[int], R: list[int], sub_key: list[int]) -> list[int]: Mixes the left and right halves of the block.
• swapper(L: list[int], R: list[int]) -> tuple[list[int]]: Swaps the left and right halves of the block.

• dec_block(block: list[int]) -> list[int]: Decrypts a 64-bit block using DES.

• encrypt(msg_str: str) -> bytes: Encrypts the entire message, padding if necessary.
• decrypt(msg_bytes: bytes) -> str: Decrypts the entire message, removing padding if necessary.

1. Initialization:
   • Create an instance of the KeyManager to read or generate keys.
   • Instantiate the DES class with the key.
2. Key Generation: Generate the round subkeys using the key_generation method.
3. Encryption (Server):
   • Receive a message from the client.
   • Encrypt the message using encrypt method.
   • Send the ciphertext back to the client.
4. Decryption (Client):
   • Receive the ciphertext from the server.
   • Decrypt the ciphertext using the decrypt method.
   • Display the decrypted message.

• Properly handle exceptions such as key length, block size, and input validation.