Fix SORT_REGULAR transitivity for mixed types

[jmarble]

Problem

array_unique() with SORT_REGULAR was missing duplicates, and sort() was producing inconsistent results depending on input order when comparing mixed types (numeric strings, non-numeric strings, integers, doubles).

The root cause: SORT_REGULAR was using PHP's comparison operators (which are non-transitive by design) directly in sorting algorithms that require transitive comparisons to function correctly.

When comparing these types, the comparison created cycles:

• "5" < "10" (numeric: 5 < 10)
• "10" < "3A" (lexicographic: '1' < '3')
• "5" > "3A" (lexicographic: '5' > '3') Creates a cycle

This violated the fundamental requirement of sorting algorithms: the comparison function must be transitive. This affected not only scalar strings but also nested arrays and objects with string properties.

Solution

Added EG(transitive_compare_mode) flag to zend_executor_globals that enforces transitive comparison during sorting operations, with consistent ordering that matches PHP 8+ semantics: empty-strings < numeric-types < numeric-strings < non-numeric.

Modified three comparison functions to check this flag:

• zendi_smart_strcmp() - handles string-to-string comparisons
• compare_long_to_string() - handles integer-to-string comparisons
• compare_double_to_string() - handles double-to-string comparisons

The flag is properly initialized in init_executor() and uses save/restore pattern in php_array_data_compare_unstable_i() to handle reentrancy correctly.

Important: This fix does not change the behavior of comparison operators like <=>, maintaining backward compatibility. The fix only affects sorting and array operations with SORT_REGULAR.

Tests

Added two comprehensive tests:

• gh20262.phpt - Bug reproduction test covering scalars, objects, and nested arrays
• sort/sort_variation_numeric_strings.phpt - Edge case tests for numeric string handling

All existing array sorting tests pass without modification!

---

Previous attempts:

• Fix #20262: SORT_REGULAR transitivity violation with mixed numeric/non-numeric strings #20305
• Fix GH-20262: array_unique() SORT_REGULAR fails to deduplicate with mixed strings #20273

This PR provides the complete solution.

Fixes #20262

[jmarble]

@devnexen @nielsdos I reached out to @nikic regarding the four failed tests.

Update: Fixed! The tests were failing because:

1. Empty strings weren't being handled as a special case (they should sort before numbers)
2. The transitive_compare_mode flag wasn't initialized (caused issues on Windows ZTS)

[withinboredom]

Nice! Some suggested additional tests that could help:

$a = ["", "0", "00", "A"];
$b = ["A", "00", "0", ""];
sort($a, SORT_REGULAR);
sort($b, SORT_REGULAR);
var_dump($a === $b); // expect true
// and expected order: ["", "0", "00", "A"]?

$a = [" 5", "+5", "-0", "0", "A"];
sort($a, SORT_REGULAR);
// expect numeric ones before "A", retaining numeric ordering: ["-0","0","+5"," 5","A"] and stable or no (+5 vs [space]5 insertion order)?

$a = ["5e2", "500", "NAN", "INF", "-INF"];
sort($a, SORT_REGULAR);
// So: ["500","5e2", "-INF","INF","NAN"]?

$a = ["0x10", "16", "0b10000"];
sort($a, SORT_REGULAR);
// expect: ["16", "0b10000", "0x10"]?

$a = [10, "3A", 5, "10", ""];
sort($a, SORT_REGULAR);
// expect: ["", 5, 10, "10", "3A"]?

$a = ["9223372036854775807", "9223372036854775808", 9223372036854775807];
sort($a, SORT_REGULAR);
// ensure consistency across LONG_MAX vs double promotions