[Memorize] Add python binding for Memorize

Context

This MR simply adds the Python binding for the Memorize_Op class and the Memorize() factory function.

Detailed modifications

Added:

• pybind_Memorize.cpp: the binding initialization function

Updated:

• pybind_core.cpp: call the initialization function
• Memorize.hpp: changed inherited Registrable template type to ...std::shared_ptr<OperatorImpl>... instead of ...std::unique_ptr<OperatorImpl>.... See questions below.

Questions to reviewers

I changed the inheritance of Memorize_Op in Memorize.hpp to Registrable<Memorize_Op, ..., std::shared_ptr<OperatorImpl>...), i.e. a shared_ptr instead of a unique_ptr, as it is what I observed for the other python binded operators.

Without this change it is not possible to compile the declare_registrable<Memorize_Op>(m, "MemorizeOp") call due to type conflicts within the Registrable templates.

Though, actually I do not understand the implications, can you clarify please?

OK, see answer below.

TODO

• Should we inherit from Registrable<Memorize_Op, ..., std::shared_ptr<OperatorImpl>...) or leave as it was: Registrable<Memorize_Op, ..., std::unique_ptr<OperatorImpl>...)? Yes, see answer below