feat: add bounded structure-aware Behavior Tree XML diff

CMakeLists.txt

@@ -143,6 +143,7 @@ list(APPEND BT_SOURCE
     src/script_parser.cpp
     src/json_export.cpp
     src/xml_parsing.cpp
+    src/xml_diff.cpp
 
     src/actions/test_node.cpp
     src/actions/sleep_node.cpp

include/behaviortree_cpp/xml_diff.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <string>
+#include <string_view>
+
+#include "behaviortree_cpp/exceptions.h"
+
+namespace BT
+{
+
+enum class XMLDiffFormat
+{
+  PlainText,
+  Markdown
+};
+
+/**
+ * @brief Render a structural review diff between two Behavior Tree XML documents.
+ *
+ * @throws RuntimeError if either document is malformed XML.
+ */
+[[nodiscard]] std::string RenderXMLDiff(std::string_view before_xml,
+                                        std::string_view after_xml,
+                                        XMLDiffFormat format = XMLDiffFormat::Markdown);
+
+}  // namespace BT