bpo-40302: Replace PY_INT64_T with int64_t (GH-19573)

* Replace PY_INT64_T with int64_t
* Replace PY_UINT32_T with uint32_t
* Replace PY_UINT64_T with uint64_t

sha3module.c no longer checks if PY_UINT64_T is defined since it's
always defined and uint64_t is always available on platforms
supported by Python.