rust-cpython: move py_shared_state to PySharedRefCell object...
rust-cpython: move py_shared_state to PySharedRefCell object
The goal of this series is to encapsulate more "py_shared" thingy and
reduce the size of the macro, which is hard to debug.
Since py_shared_state manages the borrowing state of the object owned by
PySharedRefCell, this change makes more sense. If a PyObject has more than
one data to be leaked into Python world, each PySharedState should incref
the parent PyObject, and keep track of the corresponding borrowing state.
