Refactor app container to modularity.

lib/packages/Inpsyde/Modularity/Module/ServiceModule.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WooCommerce\PayPalCommerce\Vendor\Inpsyde\Modularity\Module;
+
+interface ServiceModule extends Module
+{
+
+    /**
+     * Return application services' factories.
+     *
+     * Array keys will be services' IDs in the container, array values are callback that
+     * accepts a PSR-11 container as parameter and return an instance of the service.
+     * Services are "cached", so the given factory is called once the first time `get()` is called
+     * in the container, and on subsequent `get()` the same instance is returned again and again.
+     *
+     * @return array<string, callable(\WooCommerce\PayPalCommerce\Vendor\Psr\Container\ContainerInterface $container):mixed>
+     */
+    public function services(): array;
+}