[!!!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.

src/Graphs/DependencyInjection/Configuration.php

@@ -19,7 +19,7 @@
 
 use function assert;
 
-class Configuration implements ConfigurationInterface
+final class Configuration implements ConfigurationInterface
 {
     public function getConfigTreeBuilder(): TreeBuilder
     {

src/Graphs/DependencyInjection/GraphsExtension.php

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

src/Graphs/Nodes/UmlNode.php

@@ -15,7 +15,7 @@
 
 use phpDocumentor\Guides\Nodes\TextNode;
 
-class UmlNode extends TextNode
+final class UmlNode extends TextNode
 {
     private string $caption = '';
 

src/Graphs/Renderer/PlantumlRenderer.php

@@ -24,7 +24,7 @@
 use function sys_get_temp_dir;
 use function tempnam;
 
-class PlantumlRenderer implements DiagramRenderer
+final class PlantumlRenderer implements DiagramRenderer
 {
     public function __construct(private readonly LoggerInterface $logger, private readonly string $plantUmlBinaryPath)
     {