Use generic NonZero.

Author: reitermarkus

core/src/iter/adapters/step_by.rs

@@ -1,7 +1,7 @@
 use crate::{
     intrinsics,
     iter::{from_fn, TrustedLen, TrustedRandomAccess},
-    num::NonZeroUsize,
+    num::NonZero,
     ops::{Range, Try},
 };
 
@@ -42,10 +42,10 @@ impl<I> StepBy<I> {
     /// The `step` that was originally passed to `Iterator::step_by(step)`,
     /// aka `self.step_minus_one + 1`.
     #[inline]
-    fn original_step(&self) -> NonZeroUsize {
+    fn original_step(&self) -> NonZero<usize> {
         // SAFETY: By type invariant, `step_minus_one` cannot be `MAX`, which
         // means the addition cannot overflow and the result cannot be zero.
-        unsafe { NonZeroUsize::new_unchecked(intrinsics::unchecked_add(self.step_minus_one, 1)) }
+        unsafe { NonZero::new_unchecked(intrinsics::unchecked_add(self.step_minus_one, 1)) }
     }
 }
 
@@ -231,12 +231,12 @@ unsafe impl<I: Iterator> StepByImpl<I> for StepBy<I> {
     #[inline]
     default fn spec_size_hint(&self) -> (usize, Option<usize>) {
         #[inline]
-        fn first_size(step: NonZeroUsize) -> impl Fn(usize) -> usize {
+        fn first_size(step: NonZero<usize>) -> impl Fn(usize) -> usize {
             move |n| if n == 0 { 0 } else { 1 + (n - 1) / step }
         }
 
         #[inline]
-        fn other_size(step: NonZeroUsize) -> impl Fn(usize) -> usize {
+        fn other_size(step: NonZero<usize>) -> impl Fn(usize) -> usize {
             move |n| n / step
         }