Add Gronsfeld cipher implementation

[SpandanM110]

Describe your change:

This pull request adds new functionality to the ciphers/gronsfeld.py file by implementing the Gronsfeld cipher for both encryption and decryption. The main changes include the addition of two functions: gronsfeld_encrypt and gronsfeld_decrypt, along with an example usage section.

New functionality:

• ciphers/gronsfeld.py: Added the gronsfeld_encrypt function to encrypt plaintext using the Gronsfeld cipher.
• ciphers/gronsfeld.py: Added the gronsfeld_decrypt function to decrypt ciphertext using the Gronsfeld cipher.

Example usage:

• ciphers/gronsfeld.py: Included an example usage section to demonstrate how to use the gronsfeld_encrypt and gronsfeld_decrypt functions. This commit adds the implementation of the Gronsfeld cipher, which includes functions for encrypting and decrypting messages using a numeric key. The gronsfeld_encrypt function takes a plaintext message and a key as input and returns the encrypted message. The gronsfeld_decrypt function takes a ciphertext message and a key as input and returns the decrypted message. The implementation also includes an example usage section that demonstrates how to encrypt and decrypt a message using the Gronsfeld cipher.

Closes #11835

[SpandanM110]

Contributions for the Hacktoberfest and will be working for other language that is for Javascript as well.

[cclauss]

Closing tests_are_failing PRs to prepare for Hacktoberfest