fix: stabilize blackbox tests

[simPod]

Summary

• Configure PHP-FPM to listen on port 9000 on all container interfaces
• Fix BlackBox nginx 502 responses caused by nginx connecting to php-fpm:9000 while FPM only listened on loopback inside its own container
• Reserve APCng summary observation indexes with the atomic apcu_inc() return value to avoid losing concurrent observations

Verification

• docker compose up -d --build
• docker compose run --rm phpunit env ADAPTER=apc vendor/bin/phpunit --filter gaugesShouldBeOverwritten tests/Test/BlackBoxTest.php
• docker compose run --rm phpunit env ADAPTER=apc vendor/bin/phpunit tests/Test/BlackBoxTest.php
• docker compose run --rm phpunit env ADAPTER=apcng vendor/bin/phpunit tests/Test/BlackBoxTest.php

[Copilot]

Pull request overview

Configures the PHP-FPM container to accept FastCGI connections from other containers (not just loopback), resolving Nginx-to-PHP-FPM connectivity issues that previously manifested as 502s in the blackbox Nginx setup.

Changes:

• Updated PHP-FPM pool config to listen on TCP port 9000 on the container’s interfaces rather than 127.0.0.1:9000.

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[LKaemmerling]

Thank you!