Consolidate PHPUnit tests into tests/phpunit directory

Move test-admin.php and test-core.php from tests/ to tests/phpunit/
to match phpunit.xml configuration which only scans tests/phpunit/.

This fixes PHPUnit test discovery issues where tests were being
skipped because they were in the wrong directory.

All test files now in: tests/phpunit/
- test-admin.php
- test-core.php
- test-multisite.php
- bootstrap.php

🤖 Generated with [Qoder][https://qoder.com]

tests/bootstrap.php

@@ -1,29 +0,0 @@
-<?php
-/**
- * PHPUnit bootstrap file
- *
- * @package WPALLSTARS\PluginStarterTemplate
- */
-
-// First, we need to load the composer autoloader so we can use WP Mock.
-require_once dirname(__DIR__) . '/vendor/autoload.php';
-
-// No need to import WP_Mock classes here
-
-// Now call the bootstrap method of WP Mock.
-WP_Mock::bootstrap();
-
-/**
- * Now we define a few constants to help us with testing.
- */
-define('WPST_PLUGIN_DIR', dirname(__DIR__) . '/');
-define('WPST_PLUGIN_URL', 'http://example.org/wp-content/plugins/wp-plugin-starter-template/');
-define('WPST_VERSION', '0.1.0');
-
-/**
- * Now we include any plugin files that we need to be able to run the tests.
- * This should be files that define the functions and classes you're going to test.
- */
-require_once WPST_PLUGIN_DIR . 'includes/class-core.php';
-require_once WPST_PLUGIN_DIR . 'includes/class-plugin.php';
-require_once WPST_PLUGIN_DIR . 'admin/lib/admin.php';