Add correctness tests to the CMOX crate

[bifurcation]

The current tests of the CMOX crate are "round-trip" tests, which only test that the library interoperates with itself. For example, that it can decrypt what it encrypts. These tests don't verify that any actual cryptography is going on.

To fix this gap, we should add correctness tests, in which we use test vectors to verify that the crypto library is doing the right operations. NIST publishes test vectors for a lot of algorithms in their ACVP repo. I don't think we need to be super ambitious here, since we're just verifying that we're calling the APIs correclty. It would be enough to check one or two test vectors for each algorithm.