Add Base91 encoding and decoding operations

[ialejandrozalles]

• Implement Base91 algorithm using 91 printable ASCII characters
• Add ToBase91 operation for encoding data to Base91
• Add FromBase91 operation for decoding Base91 strings
• Base91 provides ~23% better space efficiency than Base64
• Support for Unicode text, emojis, and binary data
• Full round-trip encoding/decoding compatibility
• Integration with CyberChef operation system

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Izai Alejandro Zalles Merino seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}