feat: implement command bus with attribute-based handler resolution and add example command and handler (#27)

Reviewed-on: #27
Co-authored-by: Ron Rise <ron@siteworxpro.com>
Co-committed-by: Ron Rise <ron@siteworxpro.com>

tests/CommandBus/AttributeLocatorTest.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Siteworxpro\Tests\CommandBus;
+
+use League\Tactician\Exception\CanNotInvokeHandlerException;
+use Siteworxpro\App\CommandBus\AttributeLocator;
+use Siteworxpro\App\CommandBus\Commands\ExampleCommand;
+use Siteworxpro\App\CommandBus\Handlers\ExampleHandler;
+use Siteworxpro\Tests\Unit;
+
+class AttributeLocatorTest extends Unit
+{
+    private const array HANDLERS = [
+        ExampleCommand::class => ExampleHandler::class,
+    ];
+
+    public function testResolvesFiles(): void
+    {
+        $attributeLocator = new AttributeLocator();
+
+        foreach (self::HANDLERS as $command => $handler) {
+            $class = $attributeLocator->getHandlerForCommand($command);
+            $this->assertInstanceOf($handler, $class);
+        }
+    }
+
+    public function testThrowsOnCannotResolve(): void
+    {
+        $attributeLocator = new AttributeLocator();
+
+        $this->expectException(CanNotInvokeHandlerException::class);
+        $attributeLocator->getHandlerForCommand('NonExistentCommand');
+    }
+}