Adapted from XRay's workflow. Tests run on PHP 7.3 through 8.4: the
library supports 7.1+, but PHPUnit 9.6 needs 7.3. There's no committed
composer.lock, so dependencies are resolved per PHP version and the
cache is keyed on composer.json. ext-sockets is enabled so the resolver
test covers hosts-file IPv6 lookups.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>