gh-89653: PEP 670: unicodeobject.h uses _Py_CAST() (#92696)

Use _Py_CAST() and _Py_STATIC_CAST() in macros wrapping static inline
functions of unicodeobject.h.

Change also the kind type from unsigned int to int: same parameter
type than PyUnicode_FromKindAndData().

The limited API version 3.11 no longer casts arguments to expected
types.