Mark the HeadingRenderer class as internal

This will reduce the maintenance burden and ensure more controlled usage within the core library. If future user needs arise, we will consider revisiting this decision.

packages/framework/src/Markdown/Processing/HeadingRenderer.php

@@ -14,6 +14,8 @@
 /**
  * Renders a heading node, and supports built-in permalink generation.
  *
+ * @internal This class is an internal implementation detail of our Markdown processing and is not indented for use outside of the framework.
+ *
  * @see \League\CommonMark\Extension\CommonMark\Renderer\Block\HeadingRenderer
  */
 class HeadingRenderer implements NodeRendererInterface