[php-src] PR #24515: Fix gh 24497 hard limit default

Pull Request: https://github.com/php/php-src/pull/24515 Author: theworker02 ## Summary Fixes #24497. This pull request corrects the default configuration value reported by memory_hard_limit_percent, which was introduced as part of PHP's memory-limit security hardening. Previously, the directive was registered with a NULL default, causing ini_get('memory_hard_limit_percent') to return an empty string instead of the expected -1. ## Changes - Updated the directive registration in main/main.c to use "-1" instead of NULL. - Added PHPT tests covering configuration reporting and runtime overrides. - Added a GitHub Actions workflow to build PHP and execute the regression tests. ## Expected Behavior ```php var_dump(ini_get('memory_hard_limit_percent')); ``` Expected output: ```text string(2) "-1" ``` The change is intended to make the reported default consistent with the existing automatic hard-limit behavior, without modifying the underlying memory allocation algorithm. ## Testing - PHP CLI build and focused regression-test workflow completed successfully on the contributor's fork. - GitHub Actions: https://github.com/theworker02/php-src-patch/actions/runs/39684425665 ## Related Issue Fixes #24497