gh-99845: Use size_t type in __sizeof__() methods (#99846)

gh-99845: Use size_t type in __sizeof__() methods (#99846)

The implementation of __sizeof__() methods using _PyObject_SIZE() now
use an unsigned type (size_t) to compute the size, rather than a signed
type (Py_ssize_t).

Cast explicitly signed (Py_ssize_t) values to unsigned type
(Py_ssize_t).