fix(cloud): centralize test-double autoloading via composer files

Move InMemoryRepositories.php from require_once workaround to composer
files-autoload. Enables PSR-4 autoloading of test-double classes and
scales for 5+ future test files. All 8 tests pass with require_once removed.

cloud/composer.json

@@ -4,5 +4,8 @@
   "require": { "php": ">=8.2" },
   "require-dev": { "phpunit/phpunit": "^11" },
   "autoload": { "psr-4": { "App\\": "src/" } },
-  "autoload-dev": { "psr-4": { "App\\Tests\\": "tests/" } }
+  "autoload-dev": {
+    "psr-4": { "App\\Tests\\": "tests/" },
+    "files": ["tests/Support/InMemoryRepositories.php"]
+  }
 }

cloud/tests/RepositoryContractTest.php

@@ -1,7 +1,6 @@
 <?php
 declare(strict_types=1);
 namespace App\Tests;
-require_once __DIR__ . '/Support/InMemoryRepositories.php';
 use App\Tests\Support\{InMemoryNonceRepository, InMemoryEventRepository, InMemoryRateLimiter};
 use PHPUnit\Framework\TestCase;