PERF: Use python integer on _count_reduce_items (numpy#21465)

Small micro-optimization, since using Python integers is generally a bit faster in the loop.
The effect is small, so this could undone if anyone figures it is cleaner the other way.

Author: eendebakpt

numpy/core/_methods.py

@@ -71,9 +71,10 @@ def _count_reduce_items(arr, axis, keepdims=False, where=True):
             axis = tuple(range(arr.ndim))
         elif not isinstance(axis, tuple):
             axis = (axis,)
-        items = nt.intp(1)
+        items = 1
         for ax in axis:
             items *= arr.shape[mu.normalize_axis_index(ax, arr.ndim)]
+        items = nt.intp(items)
     else:
         # TODO: Optimize case when `where` is broadcast along a non-reduction
         # axis and full sum is more excessive than needed.