Release a transit shell's C state through the new transfer kind

[EdmondDantes]

Needs true-async/php-src#20, which adds the kind this dispatches.

thread_release_transferred_object walked the shell's properties, dropped the class name and pefreed the allocation. Anything a transfer_obj handler had put in the shell's C prefix was never reached, because free_obj does not run for a shell. The TrueAsync server leaked a topic-hub reference for every room transferred into a pool task — 21,608 bytes of hub plus the persistent topic string, per hub.

The walk now resolves the shell's class by name and calls its handler with ZEND_OBJECT_TRANSFER_RELEASE before the generic cleanup. No autoload: a release runs outside a request, and a class that is not loaded cannot own anything here anyway.

The three handlers in this extension refuse the new kind explicitly. Each branches on TRANSFER and treats everything else as LOAD, so reaching that branch with a NULL default_fn would crash. Closure's snapshot is already freed by the walk itself, through the properties marker. The channel reference and the future's shared state move under protocols of their own — untangling those is a change of its own, not a side effect of this one.

Measurements

ext/async: 3 failed, all three pre-existing (__DIR__ resolves the symlink, so their include of a php-src helper four levels up misses). tests/phpt of true-async/server against a build with this change: 1 failed, pre-existing and unrelated (an h3 test whose --EXPECTF-- ends in %A).

The leak this exists for, measured on a room transferred into a ThreadPool task: definitely lost: 21,648 bytes in 2 blocks before, 0 bytes in 0 blocks after.

[EdmondDantes]

CI is red on the build step for the stated dependency, not for a defect here: the runners build php-src from the true-async branch, where the kind does not exist yet.

ext/async/future.c:768:21: error: 'ZEND_OBJECT_TRANSFER_RELEASE' undeclared

It turns green once true-async/php-src#20 lands and this branch is re-run.

[codecov]

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