docs: fix namespaces for sample classes

Author: kenjis

user_guide_src/source/database/query_builder/077.php

@@ -1,12 +1,14 @@
 <?php
 
+namespace App\Libraries;
+
 class Myclass
 {
     public $title   = 'My Title';
     public $content = 'My Content';
     public $date    = 'My Date';
 }
 
-$object = new \Myclass();
+$object = new Myclass();
 $builder->insert($object);
 // Produces: INSERT INTO mytable (title, content, date) VALUES ('My Title', 'My Content', 'My Date')

user_guide_src/source/extending/events/002.php

@@ -6,7 +6,7 @@
 Events::on('pre_system', 'some_function');
 
 // Call on an instance method
-$user = new \User();
+$user = new \App\Libraries\User();
 Events::on('pre_system', [$user, 'someMethod']);
 
 // Call on a static method

user_guide_src/source/testing/overview/006.php

@@ -1,5 +1,7 @@
 <?php
 
+namespace App\Traits;
+
 trait AuthTrait
 {
     protected function setUpAuthTrait()
@@ -15,7 +17,7 @@ protected function setUpAuthTrait()
 
 final class AuthenticationFeatureTest extends CIUnitTestCase
 {
-    use \AuthTrait;
+    use AuthTrait;
 
     // ...
 }