[DeepClone] Fix round-tripping short-lived Random\Randomizer instances on PHP 8.2

[nicolas-grekas]

Q	A
Branch?	1.x
Bug fix?	yes
New feature?	no
Deprecations?	no
Issues	-
License	MIT

This is what has been segfaulting the PHP 8.2 CI jobs since the Randomizer round-trip tests landed in #629 (and what #630 inherits).

Minimal reproducer, no polyfill involved, on PHP 8.2.31:

$state = (new Random\Randomizer(new Random\Engine\Mt19937(7)))->__serialize();
serialize($state); // SIGSEGV

Before PHP 8.3, Random\Randomizer::__serialize() returns the object's raw property table with only the table itself addref'd. Its engine entry is an IS_INDIRECT slot pointing into the object, so once the Randomizer is released the retained state dangles. php-src fixed this for 8.3 by duplicating the table (php/php-src@c5fa7696e64), but 8.2 was already security-only and the fix was never backported; 8.2.31 still crashes.

deepclone_to_array() retains exactly such a state in its payload, so round-tripping a Randomizer that does not outlive the payload segfaulted on 8.2. There is no copy-based userland fix: plain array reads copy IS_INDIRECT slots verbatim instead of resolving them (gettype() reports unknown type), which is also how the contamination is detected. The serializer is the one userland-reachable code path that resolves these slots, so when a __serialize() result is contaminated (checked while the source object is still alive, and only on PHP < 8.3), it is passed through a serialize()/unserialize() round trip to materialize real values.

No new tests: the #629 Randomizer tests are the regression tests; they segfault on PHP 8.2 before this change and pass after (suite verified green on 8.1, 8.2, 8.3 and 8.5). The nested engine becomes a fresh copy rather than a shared instance on the affected versions, matching the already-documented identity behavior of nested __serialize() states.

Companion extension fix (the with-extensions 8.2 CI legs run the tagged ext via PIE and stay red until it ships in a release): symfony/php-ext-deepclone#23

Perf note: Random\Randomizer is special-cased instead of scanned for, after auditing PHP 8.2 core for the pattern: of the internal classes whose __serialize() retains the un-duplicated property table (Randomizer, HashContext, the Random engines), only Randomizer declares a property, and only declared properties create IS_INDIRECT slots (GMP uses the legacy serialize handler, consumed while the object is alive; the date classes already duplicate). Measured on 8.2: no overhead for any other class; Randomizer itself pays one serialize round trip (~190 us for a Mt19937 state), the price of not crashing. On PHP 8.3+ the version guard makes the branch dead code. The trade-off versus scanning every internal state: a hypothetical third-party extension class combining the same pattern with declared properties would keep crashing, as it does today.

Companion extension fix (the with-extensions 8.2 CI legs run the tagged ext via PIE, fixed in v0.7.2): symfony/php-ext-deepclone#23