[php-src] PR #23808: FPM status: full OpenMetrics support with per-worker metrics

Pull Request: https://github.com/php/php-src/pull/23808 Author: 1ma Closes #9494, alternative to #12759 The former logic was quite a mess and I saw no way to fit the OpenMetrics per-worker stats into the existing control flow, so I extracted each format handling into its own static function and fpm_status_handle_request() became a simple dispatcher to the specialized handler. For text/html/xml/json these functions are a bit repetitive, but for OpenMetrics this design allows the flexibility to have a different control flow that doesn't interfere with the other formats. I tried to organize the commits to ease review, each one does a logical step and compiles and passes the tests. I also fixed a subtle bug in the existing OpenMetrics output, for phpfpm_listen_queue_length the HELP and TYPE annotations were swapped, that's why I had to amend fpm/tests/status.inc.