[php-src] PR #25111: Fix GH-25107: Preserve foreach iterators on array_unshift

Pull Request: https://github.com/php/php-src/pull/25111 Author: JoaoMarcos44 Fixes #25107. > AI-assisted contribution. The patch, regression test, and explanation were prepared with AI > assistance and checked with local builds and tests. ## Summary > Preserve foreach-by-reference iterator positions when > array_unshift() compacts holes left by deleted entries. Previously, > the iterator offset could skip an unvisited value because it still used the old slot position. > Remap iterator positions to the compacted live slots before adding the prepend offset. Arrays > without holes keep the existing path. The PHPT covers packed and mixed arrays, dense controls, > simultaneous iterators, zero and multiple prepends, and end positions. A NEWS entry records the fix. > The sparse-array path adds a slot scan when active iterators exist. Performance with many > simultaneous iterators was not measured. Related PR #24475 retains the affected fallback for arrays > with holes or active iterators. ## Validation > Target: PHP-8.4, the lowest actively supported affected branch. > Built with --enable-debug --enable-zts. > - The new regression fails before the fix and passes afterward. > - make -j1 passes. > - make test TESTS='-j1 -q --no-color --no-progress --set-timeout 120 > --show-diff ext/standard/tests/array Zend/tests/*foreach*.phpt' passes with 876 > passed and 13 skipped. No failures or warnings. The runner confirmed that the new regression and > foreach_016.phpt executed. > - The full PHP suite and Windows builds were not run. <details> <summary>Illustrated explanation</summary> > AI-generated conceptual illustration. The issue contains the executable reproduction.  [Explanation and prompt](https://github.com/JoaoMarcos44/php-src/blob/9e60fedb55c1c3bdfaeb339f1beeae2895526596/assets/array/infographic_report.md) </details>