Feature: Support union types and address deprecation of ReflectionType::getClass() (PHP 8+). (#198 by @cdosoftei and @SimonFrings)

$promise->otherwise(function (OverflowException|UnderflowException $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

Feature: Support intersection types (PHP 8.1+). (#195 by @bzikarsky)

$promise->otherwise(function (OverflowException&CacheException $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

Improve test suite, use GitHub actions for continuous integration (CI), update to PHPUnit 9, and add full core team to the license. (#174, #183, #186, and #201 by @SimonFrings and #211 by @clue)