[3.x] Add type testing

etc/qa/phpstan.neon

@@ -1,5 +1,9 @@
 parameters:
 	level: max
+	ignoreErrors:
+		-
+			message: '#Result of method ReactParallel\\Runtime\\Runtime::run\(\) \(void\) is used.#'
+			path: ../../tests/Types.php
 	ergebnis:
 		noExtends:
 			classesAllowedToBeExtended:

src/Runtime.php

@@ -26,10 +26,10 @@ public function __construct(private EventLoopBridge $eventLoopBridge, string $au
     }
 
     /**
-     * @param (Closure():?T)    $callable
+     * @param (Closure():T)|(Closure():void)    $callable
      * @param  array<int, mixed> $args
      *
-     * @return ?T
+     * @return ($callable is (Closure():T) ? T : null)
      *
      * @template T
      */

tests/Types.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+use ReactParallel\Runtime\Runtime;
+use ReactParallel\EventLoop\EventLoopBridge;
+
+use function PHPStan\Testing\assertType;
+
+$pool = Runtime::create(new EventLoopBridge());
+
+assertType('bool', $pool->run(static function (): bool {
+    return true;
+}));
+
+assertType('bool|int', $pool->run(static function (): bool|int {
+    return time() % 2 !== 0 ? true : time();
+}));
+
+assertType('null', $pool->run(static function () {
+}));