Case Preservation Issue in Chepy's Atbash Implementation (pycipher dependency)

[x9xhack]

Describe the bug:
Chepy uses pycipher to implement the Atbash cipher, but the cipher does not preserve the case of the input text during encryption. When mixed-case strings are provided, the result is always converted to uppercase, which is not the desired behavior. This issue is related to a limitation in pycipher (see pycipher issue #20 where it does not maintain the original case of the text.

Chepy should either update its implementation to preserve case or create a workaround to handle case preservation properly. Since pycipher appears to be no longer maintained, a custom solution might be needed to address this issue.

To Reproduce:

1. Use the atbash_encode function in Chepy on a mixed-case string like "zbCc;oo?|c;oAp9P%".
2. Observe that the result is converted to uppercase ("AYXX;LL?|X;LZK9K%"), ignoring the case of the input.

Expected behavior:
Chepy should preserve the case of the input text when using the Atbash cipher. Uppercase letters should remain uppercase, and lowercase letters should remain lowercase after encryption.

Screenshots:

Desktop (please complete the following information):

• OS: Linux
• Python Version: 3.11
• Chepy Version: 7.3.0

Additional context:
It seems that the issue is inherited from the pycipher library's implementation, which currently doesn't handle case preservation. Since pycipher is likely no longer maintained, it would be helpful for Chepy to consider updating its cipher implementation to handle case preservation or switch to an alternative solution.