Test interoperability with other implementations

[tomato42]

https://github.com/IETF-Hackathon/pqc-certificates

we probably will need support for DER/PEM encoding for that; that should be easy to reuse from the python-ecdsa library (which given the X25519-ML-KEM-758 combined hybrid algorithm, will be something most users of this library will want to do anyway...), but again, should be no problem having the support for them optional

[GiacomoPope]

Doing a good job of DER/PEM encoding is really hard, so this will take some careful attention

[tomato42]

Doing a good job of DER/PEM encoding is really hard, so this will take some careful attention

the library I have in python-ecdsa is super well tested and it has a really nice API, so no, I don't think it's hard 😁