Add DHKEM support and test cases

[sylph01]

Follow-up to #1062:

• Added test cases for EVP_KEM-EC / EVP_KEM-X25519 / EVP_KEM-X448 (RFC 9180 Section 4.1 — DH-Based KEM)
• Added a parameter helper for OpenSSL 3.2-3.4 so EC/X25519/X448 DHKEM works on those versions
  • On OpenSSL 3.2-3.4, DHKEM on EC/ECX keys need the operation (DHKEM) to be explicitly selected, so this adds a helper to the implementation to fill the operation parameter

Note: I left out EVP_KEM-RSA intentionally. RSA keys have a different mode of operation (RSASVE), and on OpenSSL 3.2-3.4, this needs to be explicitly set to perform RSASVE (just like DHKEM needed an explicit parameter). If there is need for this I will add it separately or in the same pull request.

[rhenium]

OpenSSL 3.3 is EOL already and 3.4 will reach EOL in 4 months: https://openssl-library.org/policies/releasestrat/index.html

To me, this looks like more of a bug fix. Fortunately, the usual suspects (Ubuntu and RHEL) appear to have skipped these versions, so I wonder if anyone would actually benefit from this workaround?

[sylph01]

If that's the case, I might just opt to remove the options helper altogether. That fix is b7d163e, and with this, the patch only includes changes to the test.

[rhenium]

I'm leaning towards not merging the default values for OSSL_KEM_PARAM_OPERATION_DHKEM. The tests seem like a good addition and passed without the change on my computer.

FWIW, I've been exploring if we could expose OSSL_PARAM from EVP_PKEY_CTX to Ruby in a generic way. I haven't had time to finish it, but a WIP branch is here: https://github.com/rhenium/ruby-openssl/commits/ky/pkey-ctx/

[rhenium]

Could you squash commits?

[sylph01]

squashed @ dfc45d3

[rhenium]

Thanks!