[GIT-PULLS] [php-src] PR #23517: PHP array_shift(): Optimize tail move on hole-free packed arrays

Pull Request: https://github.com/php/php-src/pull/23517
Author: mehmetcansahin

For a packed array without holes, removing the first element leaves a
contiguous tail. When no iterator is active, `array_shift()` now moves that
tail with a single `memmove()` instead of testing every slot for `IS_UNDEF`;
a one-element tail is moved directly to avoid the call overhead. Packed
arrays with holes, arrays with active iterators, and hash arrays keep the
existing paths.

### Benchmarks

Apple M1, Apple clang 21.0.0, `./configure --disable-all --enable-cli`
(NTS release), `php -n`, best of three in-process samples. Base
`f142b815884`, this PR `fc910a396ea`. Full scripts below.

Draining a packed int array (`$a = $base; while ($a) array_shift($a);`):

| n | repetitions | base | this PR | speedup |
|---:|------------:|-----:|--------:|--------:|
| 100 | 20,000 | 160.5 ms | 58.7 ms | 2.7× |
| 1,000 | 2,000 | 1,075.6 ms | 249.9 ms | 4.3× |
| 10,000 | 200 | 10,726.5 ms | 2,602.4 ms | 4.1× |

Two-element regression check (`$a = [0, 1]; array_shift($a);` x 100M,
exercises the direct-copy specialization): 3.528 s → 3.438 s, no tiny-array
slowdown observed.

<details>
<summary>Benchmark scripts</summary>

Draining benchmark:

```php
<?php
foreach ([100, 1000, 10000] as $n) {
    $reps = intdiv(2000000, $n);
    $base = range(0, $n - 1);
    $best = PHP_FLOAT_MAX;
    for ($run = 0; $run < 3; $run++) {
        $t = hrtime(true);
        for ($r = 0; $r < $reps; $r++) {
            $a = $base;
            while ($a) array_shift($a);
        }
        $best = min($best, (hrtime(true) - $t) / 1e6);
    }
    printf("n=%-6d drain x%-5d best: %8.1f ms\n", $n, $reps, $best);
}
```

Two-element regression check:

```php
<?php
$best = PHP_FLOAT_MAX;
for ($run = 0; $run < 3; $run++) {
    $t = hrtime(true);
    for ($i = 0; $i < 100000000; $i++) {
        $a = [0, 1];
        array_shift($a);
    }
    $best = min($best, (hrtime(true) - $t) / 1e9);
}
printf("fresh [0,1] x100M best: %.3f s\n", $best);
```

</details>

### Tests

`ext/standard/tests/array/`: 856 PASS, 12 SKIP, 0 FAIL/WARN on both the
release NTS build and a Debug+ZTS build (hashtable consistency assertions
enabled). The new test covers packed arrays with holes, which keep the
slot-testing loop.

> Parts of this description were drafted with LLM assistance and reviewed by
> the author, per the "LLM usage in GitHub comments" section of
> CONTRIBUTING.md. All results were produced and verified locally.