Deduplicate testsuite

[est31]

It would be nice if we could deduplicate the code that creates various test cases for botan, rustls, and openssl. I.E. they implement a trait and this trait is then used by the testing code. The hard part would be that ideally we still represent each resulting test via a rust test, instead of having just one big test for botan, one big one for rustls, and one big for openssl. I wonder how this can be done.