[php-src] PR #24585: Fix GH-24577: CE-cache flag on interned class name visible before map_ptr offset

Pull Request: https://github.com/php/php-src/pull/24585 Author: prateekbhujel Fixes GH-24577. In Zend Engine and OPcache, class entry (CE) caching stores the map_ptr offset in type_name->gc.refcount and tags the string with IS_STR_CLASS_NAME_MAP_PTR. In multi-process environments like PHP-FPM, concurrent compilation on a cold cache could allow worker processes to observe IS_STR_CLASS_NAME_MAP_PTR before the offset store was committed or reordered, causing readers to pick up refcount 2 (the initial refcount for SHM interned strings). Because (2 - 1) / sizeof(void*) == 0 < CG(map_ptr_last), ZSTR_VALID_CE_CACHE accepted offset 2, leading to an unaligned read of bogus pointer bytes at (map_ptr_base + 2) and SIGSEGV in object_init_ex. This patch addresses both the validation invariant and memory ordering across the engine: 1. **Harden ZSTR_VALID_CE_CACHE()**: Strictly reject GC_REFCOUNT(s) <= 2 in Zend/zend_types.h, matching the guarantee in zend.c and zend_persist.c that valid map_ptr offsets are always > 2. 2. **Correct store order in zend.c**: In zend_alloc_ce_cache(), set GC_SET_REFCOUNT before setting IS_STR_CLASS_NAME_MAP_PTR. 3. **Acquire/Release memory fences**: Add acquire-release thread fences between publishing the refcount and setting IS_STR_CLASS_NAME_MAP_PTR across Zend/zend.c, ext/opcache/zend_persist.c, ext/opcache/ZendAccelerator.c, and the reader in Zend/zend_execute_API.c. 4. **Regression test**: Add ext/opcache/tests/gh24577.phpt covering concurrent compilation and instantiation under OPcache.