Standardize nullable type hints to 'null|Type' order

Refactors type hints and docblocks across the codebase to consistently use the 'null|Type' order for nullable types, improving code readability and alignment with modern PHP standards. No functional changes are introduced; this is a documentation and type annotation update only.

Author: huangdijia

src/SignalRegistry.php

@@ -49,9 +49,9 @@ public function register(int|array $signo, callable $signalHandler): void
     }
 
     /**
-     * @param int|int[]|null $signo
+     * @param null|int|int[] $signo
      */
-    public function unregister(int|array|null $signo = null): void
+    public function unregister(null|int|array $signo = null): void
     {
         match (true) {
             // Unregister all signals

src/Traits/InteractsWithSignals.php

@@ -36,7 +36,7 @@ protected function trap(array|int $signo, callable $callback): void
         $this->signalRegistry->register($signo, $callback);
     }
 
-    protected function untrap(array|int|null $signo = null): void
+    protected function untrap(null|array|int $signo = null): void
     {
         $this->signalRegistry?->unregister($signo);
     }