Fix package test runs and trim to a minimal package set

Tests:
- Derive PHP extensions from each package's composer.json in CI and run
  on PHP 8.4 (client and queue require >=8.4)
- Install with --ignore-platform-reqs, matching upstream package CI
- Run suites with a compose 'tests' service inside containers
- Scope http's composer test to the unit suite; e2e moves to test:e2e
- Fix platform tests against the PSR header API in http 2.0.0-rc5
- Allow workflow_dispatch with a package list

Packages: keep cli, client, http, platform, queue; di, fetch, registry
and system can be re-imported later.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: loks0n

composer.json

@@ -27,7 +27,8 @@
         "analyze": "vendor/bin/phpstan analyse -c phpstan.neon --memory-limit 512M",
         "refactor": "vendor/bin/rector process",
         "refactor:check": "vendor/bin/rector process --dry-run",
-        "test": "vendor/bin/phpunit --configuration phpunit.xml"
+        "test": "vendor/bin/phpunit --configuration phpunit.xml --testsuite unit",
+        "test:e2e": "vendor/bin/phpunit --configuration phpunit.xml --testsuite e2e-fpm,e2e-swoole"
     },
     "require": {
         "php": ">=8.3",