Case Preservation Issue in pycipher.Atbash Cipher

[x9xhack]

Problem:
The pycipher.Atbash cipher does not preserve the case of the input text during encryption. When encrypting mixed-case strings, the output is always converted to uppercase, which may not be the desired behavior.

Steps to Reproduce:

Use the Atbash cipher on a string with mixed case, such as "zbCc".
Observe that the result is converted to uppercase, even though the input string contains both lowercase and uppercase characters.

Expected Behavior:
The Atbash cipher should preserve the case of the input text, meaning that lowercase letters should remain lowercase and uppercase letters should remain uppercase after encryption.

Actual Behavior:
The Atbash cipher converts all letters to uppercase, ignoring the case of the input text.