Feature request: CSR decoding and encoding

**Is your feature request related to a problem? Please describe.**
It's just nice to have all tools I'd need in one place.

**Describe the solution you'd like**
A decoder and encoder for Certificate Signing Requests (CSRs) like https://certlogik.com/decoder/

**Describe alternatives you've considered**
Using other tools

**Additional context**

No files, tests, or entry points are named. Start by reviewing CyberChef’s existing operation structure and the linked CSR decoder’s behavior; determine how CSR decoding and encoding should fit the project. Done means CyberChef provides both capabilities with appropriate coverage.

Written by the indexing model from the issue text.