Fixing Segfault for Py >= 3.10 due to PY_SSIZE_T_CLEAN

[Cleric-K]

When using s# formats with Py_BuildValue, since 3.10 PY_SSIZE_T_CLEAN has to be defined before including Python.h. Otherwise Py_BuildValue returns 0 which results in Segfault.

See https://bugs.python.org/issue36381