Support for storing private keys as seeds

[tomato42]

The new draft-ietf-lamps-kyber-certificates-06 mandates storing the private key as the un-expanded seed instead of expanded value. Add a public API that allows expanding keys from the seed and update the example scripts with support for that.

Builds on top of #80

Not interoperable with oqsprovider: open-quantum-safe/oqs-provider#613 or openssl: openssl/openssl#25885

[GiacomoPope]

im ok with adding the seed check, but this should be included in some tests somewhere? Also, we don't need the interopt code to be included in this PR?

[tomato42]

but this should be included in some tests somewhere?

you mean you'd like unit tests or you'd like interoperability tests?

Also, we don't need the interopt code to be included in this PR?

yes, I should probably add the test vectors from the draft

[GiacomoPope]

i mean i dont think this PR should be about interoperability and rather just adding this new keygen from seed function, which should be tested in the unit tests for ML-KEM

[tomato42]

i mean i dont think this PR should be about interoperability and rather just adding this new keygen from seed function, which should be tested in the unit tests for ML-KEM

aah, split up the addition of the API, sure, can do a separate PR for that alone

[tomato42]

The PR adding API alone, together with test coverage: #90