feat: implement command bus with attribute-based handler resolution and add example command and handler

tests/GrpcHandlers/GreeterHandlerTest.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Siteworxpro\Tests\GrpcHandlers;
+
+use Siteworxpro\Tests\Unit;
+use Spiral\RoadRunner\GRPC\ContextInterface;
+
+class GreeterHandlerTest extends Unit
+{
+    public function testSayHello(): void
+    {
+        $request = new \GRPC\Greeter\HelloRequest();
+        $request->setName('World');
+
+        $context = \Mockery::mock(ContextInterface::class);
+
+        $handler = new \Siteworxpro\App\GrpcHandlers\GreeterHandler();
+        $response = $handler->SayHello($context, $request);
+        $this->assertEquals('Hello World', $response->getMessage());
+    }
+}