fix insert exclude highlight

packages/notus/lib/src/heuristics/insert_rules.dart

     final attributes = previous.attributes;
     final hasLink =
         (attributes != null && attributes.containsKey(NotusAttribute.link.key));
+    final hasHighLight = (attributes != null && attributes.containsKey(NotusAttribute.highlight.key));
+    if (hasHighLight) {
+      attributes.remove(NotusAttribute.highlight.key);
+    }
     if (!hasLink) {
       return Delta()
         ..retain(index)