[php-src] PR #24005: ext/standard: Pin lazy proxy instances while reading properties

Pull Request: https://github.com/php/php-src/pull/24005 Author: iliaal serialize() and var_export() take an initialized lazy proxy's real property table without holding that instance. User code during __sleep() name resolution, or while exporting properties, can reset the proxy and free the instance before those properties are read. The real instance is now pinned until the property table is released. var_dump() and debug_zval_dump() already addref the instance in their debug info. The test keeps replacement objects alive so an unpatched build serializes the reused values.