Rollup merge of #158282 - ArhanChaudhary:unchecked-subslice, r=tgross35,jhpratt

slice_split_once: bounds check optimization note

Tracking issue: #112811

~~Use unchecked sub-slicing operations for `<T>::split_once` and `<T>::rsplit_once`.~~
Note that unchecked sub-slicing operations are equivalent to the current checked sub-slicing operations.

Author: jhpratt

library/core/src/slice/mod.rs

@@ -2530,6 +2530,7 @@ impl<T> [T] {
         F: FnMut(&T) -> bool,
     {
         let index = self.iter().position(pred)?;
+        // Slice bounds checks optimized are away (as of June 2026)
         Some((&self[..index], &self[index + 1..]))
     }
 
@@ -2558,6 +2559,7 @@ impl<T> [T] {
         F: FnMut(&T) -> bool,
     {
         let index = self.iter().rposition(pred)?;
+        // Slice bounds checks optimized are away (as of June 2026)
         Some((&self[..index], &self[index + 1..]))
     }