[php-src] PR #24644: Fix GH-23859: Reset map pointer watermark in accel_activate()

Pull Request: https://github.com/php/php-src/pull/24644 Author: aasul Fixes #23859 i looked into the map pointer growth after repeated opcache_reset() calls and found that surviving FPM workers could keep an outdated CG(map_ptr_last) value after a restart when those workers cached new scripts the old watermark would get published back into shared memory causing the map pointer table to keep growing after each reset the fix resets the local watermark during activation while keeping startup and preloaded slots intact i also added an FPM regression test using two separate workers to make sure the map pointer count stays stable when another worker triggers a reset the test fails on the original code and passes with the fix, i also ran it 20 times without any failures after 24 reset cycles the original version went from 933 to over 18000 map pointer slots while the patched version stayed at 933 NTS and ZTS both passed 6031 tests with no failures and i also checked concurrent FPM requests, worker replacement, preloading, JIT and ASan LeakSanitizer still reported some allocations during worker shutdown but the same ones also appeared on unchanged builds so nothing new seems to have been introduced i haven't tested Windows, 32 bit platforms or threaded web SAPIs > investigation and testing were assisted by AI and fully reviewed by human eyes.