… in the face of concurrent mutators (python#118454)

Add _PyType_LookupRef and use incref before setting attribute on type
Makes setting an attribute on a class and signaling type modified atomic
Avoid adding re-entrancy exposing the type cache in an inconsistent state by decrefing after type is updated

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454

Python 3.14 introduced a new assertion that prevents us from using
PyObject_GenericSetAttr directly in our meta type. To work around
this, we manipulate the type dict directly.

This workaround is a simplified variant of Cython's workaround from
cython/cython#6325.

The relevant Python change is in
python/cpython#118454