feat(smp): add SerializableBase for MPI population transfer

[evvaletov]

Summary

Adds SerializableBase<T>, a template wrapper that makes any type T
serializable via ParadisEO's eoserial::Persistent interface.

Motivation

The MPI island model (#86) needs to transfer eoPop<EOT> between MPI
ranks. ParadisEO's serialization framework (eoserial) provides
pack()/unpack() for converting objects to/from a JSON-like intermediate
representation, but eoPop doesn't directly implement
eoserial::Persistent. SerializableBase bridges this gap — it wraps any
T that has eoserial support and exposes the Persistent interface for
use with eo::mpi's send/recv.

Changes

File	Change
smp/src/SerializableBase.h	New — class declaration
smp/src/SerializableBase.tpp	New — template implementation
smp/src/smp.h	Added #include <SerializableBase.h>

[nojhan]

Seems like a good idea.

I don't recall the specifics (I worked on that a... long time ago), but why do we have a JSON serialization, apart from the regular one (the one using printOn & readFrom)? The regular one also seems more compact. And why not using a digital serialization instead of text-based one (which would be faster)?

[evvaletov]

Rebased onto HEAD.

On the serialization choice: printOn/readFrom is flat text I/O without structural metadata, so reconstructing nested types (populations of multi-objective individuals with objective vectors, fitness values, and diversity metrics) would require reimplementing what eoserial already handles recursively through Persistent::pack/unpack.

On binary vs text: fair point. The eoserial module only has a JSON backend, so adding binary would mean either extending eoserial or building a parallel serialization path, both larger changes than this PR warrants. In practice, the migrated populations are small (a few individuals per event, not the full population), so the overhead is modest relative to evaluation cost. That said, a binary serialization path for MPI transfers would be a worthwhile future improvement.

[nojhan]

I see, I forgot about the recursive part, that's a killer feature. This seems good to me. Ask for review when you're ready.