test: check PHP inside FrankenPHP, cover install checks, tidy test files

[stasadev]

Short Summary (TL;DR)

Tests now check PHP inside FrankenPHP (not only ddev php), cover the install checks, and are shorter, with clearer test file names.

The Issue

Most PHP checks ran through ddev php (the command line), which doesn't prove FrankenPHP sees the same settings. HTTPS behind the router, ddev xdebug on reaching FrankenPHP, worker state and the install.yaml checks were untested. health_checks also repeated the same header checks four times.

How This PR Solves The Issue

• New server-info.php: prints settings as FrankenPHP sees them. Tests use it to check:
  • sapi=frankenphp
  • HTTPS, SERVER_PORT and REQUEST_SCHEME through the router and through the direct host ports
  • timezone and .ddev/php ini settings
  • extensions, including after ddev xdebug, xhprof and blackfire on
  • memory_limit from FRANKENPHP_CONFIG
• Worker test: checks that X-Request-Count grows between requests.
• ddev logs -s web: must not contain the "Caddyfile input is not formatted" warning.
• New test: ddev add-on get must reject PHP 8.1 and an old FRANKENPHP_DEBIAN_CODENAME in .ddev/.env.web.
• health_checks: now uses small helpers (refute_php_warnings, assert_frankenphp_headers, assert_server_info) and one extension list, one name per line.
• Test file renames:
  • index-no-worker.php → index.php
  • index-worker.php → worker.php, cut from 225 to 16 lines
  • session-test.php → session.php

Manual Testing Instructions

bats tests/test.bats --filter-tags '!release'

Automated Testing Overview

The PR only changes tests.

Release/Deployment Notes

None, the add-on itself is unchanged.

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