Refactor for crypto library agility

[bifurcation]

This PR implements a simple strategy for making it possible to plug in new crypto libraries.

• crypto.h is pared back to just the things required in sframe.cpp
• crypto.cpp only has things that are invariant regardless of the cryptographic library (properties of cipher suites)
• In CMakeLists.txt, we have a switch that adds a #define indicating which crypto library to use
• Crypto library specifics are in an implementation file, here crypto_openssl11.cpp or crypto_openssl3.cpp.

[suhasHere]

nit about handy comments on few hardcoded values. Otherwise looks good to me.

[bifurcation]

macOS build is just failing because we keep getting non-upgraded runners. Proceeding with merge because it was green on a prior run and the only difference is comments.