Code style fixes and php language requirements update

Author: allflame

src/Bridge/BackgroundSpanHandler.php

@@ -5,7 +5,7 @@
 
 use Jaeger\Http\HttpMethodTag;
 use Jaeger\Http\HttpUriTag;
-use Jaeger\Span\Span;
+use Jaeger\Span\SpanInterface;
 use Jaeger\Symfony\Tag\SymfonyBackgroundTag;
 use Jaeger\Symfony\Tag\SymfonyComponentTag;
 use Jaeger\Symfony\Tag\SymfonyVersionTag;
@@ -15,12 +15,9 @@
 
 class BackgroundSpanHandler
 {
-    /**
-     * @var Span
-     */
-    private $span;
+    private ?SpanInterface $span;
 
-    private $tracer;
+    private TracerInterface $tracer;
 
     public function __construct(TracerInterface $tracer)
     {
@@ -50,6 +47,7 @@ public function flush(): BackgroundSpanHandler
             return $this;
         }
         $this->span->finish();
+        $this->span = null;
 
         return $this;
     }

src/Bridge/GlobalSpanListener.php

@@ -9,29 +9,29 @@
 
 class GlobalSpanListener implements EventSubscriberInterface
 {
-    private $handler;
+    private GlobalSpanHandler $handler;
 
     public function __construct(GlobalSpanHandler $handler)
     {
         $this->handler = $handler;
     }
 
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             RequestEvent::class => ['onRequest', 30],
             TerminateEvent::class => ['onTerminate', 4096],
         ];
     }
 
-    public function onTerminate()
+    public function onTerminate(): GlobalSpanListener
     {
         $this->handler->finish();
 
         return $this;
     }
 
-    public function onRequest(RequestEvent $event)
+    public function onRequest(RequestEvent $event): GlobalSpanListener
     {
         if (false === $event->isMasterRequest()) {
             return $this;