RC4 Cipher python implementation

[itspyguru]

1> Implement a RC4 Cipher encryption and decryption method and wrap it inside a class RC4Cipher
2> save it to rc4_cipher.py
3> put the file inside decrypto/src folder
4> submit a PR.

Sample implementation : https://github.com/pyGuru123/Decrypto/blob/main/decrypto/src/binary_cipher.py
strictly follow above implementation and PEP8 Guidelines