Addition of mls::State serialization using the existing serialization options

[BlehPoster]

Adds TLS_SERIALIZABLE recursively to all required nested structures while keeping member accessibility untouched by adding specific overloaded stream operators.
Known issue: Since serialization requires an empty/existing object, mls::State and its nested structures must be default constructible. As long as serialization is implemented outside of structures, default constructors are mandatory.
Added missing #ifdef(WITH_PQ)

The project builds locally (Linux, Clang 18), and all unit tests are passing.

[kosmakoff]

@BlehPoster I tried your code and it was not deserializing the State correctly - it did not restore public keys, and because of that the restored State failed to execute handle() for example.

I made the fix, if you're interested: kosmakoff@95c574f

[BlehPoster]

Hi @kosmakoff, sorry for the late reply, I will take a look at this.
But since this is stale for so long, I will close this and search for different solutions.