Fix test workflow issues with WP_Mock, PHP 7.0 compatibility, and code style

includes/core.php

@@ -1 +1,31 @@
 <?php
+/**
+ * Core functionality for the plugin
+ *
+ * @package WPALLSTARS\PluginStarterTemplate
+ */
+
+namespace WPALLSTARS\PluginStarterTemplate;
+
+/**
+ * Core class
+ */
+class Core {
+
+	/**
+	 * Constructor
+	 */
+	public function __construct() {
+		// Initialize hooks
+	}
+
+	/**
+	 * Example method to filter content
+	 *
+	 * @param string $content The content to filter.
+	 * @return string The filtered content.
+	 */
+	public function filter_content( $content ) {
+		return $content;
+	}
+}