[!!!TASK] Make all classes final

This library has a very large number of extension points via
interfaces and abstract classes. All other classes should not
be extended by users and shall theirfor be marked as final.

There are a few classes left that should also be marked as final
but those require some extra attention.

Author: jaapio

src/Bootstrap/DependencyInjection/BootstrapExtension.php

@@ -21,7 +21,7 @@
 
 use function dirname;
 
-class BootstrapExtension extends Extension implements PrependExtensionInterface
+final class BootstrapExtension extends Extension implements PrependExtensionInterface
 {
     /** @param mixed[] $configs */
     public function load(array $configs, ContainerBuilder $container): void

src/Bootstrap/Directives/TabDirective.php

@@ -27,7 +27,7 @@
 use function strtolower;
 use function strval;
 
-class TabDirective extends SubDirective
+final class TabDirective extends SubDirective
 {
     public function getName(): string
     {

src/Bootstrap/Directives/TabsDirective.php

@@ -27,7 +27,7 @@
 
 use function is_string;
 
-class TabsDirective extends SubDirective
+final class TabsDirective extends SubDirective
 {
     private int $tabsCounter = 0;
 

src/Bootstrap/Nodes/AbstractTabNode.php

@@ -35,7 +35,7 @@ public function getKey(): string
     {
         return $this->key;
     }
-    
+
     public function isActive(): bool
     {
         return $this->active;