Support nested keep-chomping block scalars when appending to block list

pkgs/yaml_edit/lib/src/list_mutations.dart

diff --git a/pkgs/yaml_edit/lib/src/list_mutations.dart b/pkgs/yaml_edit/lib/src/list_mutations.dart
index 2595d96..6210dfc 100644
--- a/pkgs/yaml_edit/lib/src/list_mutations.dart
+++ b/pkgs/yaml_edit/lib/src/list_mutations.dart
@@ -161,9 +161,24 @@
     if (nextNewLineIndex == -1) {
       formattedValue = getLineEnding(yaml) + formattedValue;
     } else {
-      if (lastNode is YamlScalar &&
-          (lastNode.style == ScalarStyle.LITERAL ||
-              lastNode.style == ScalarStyle.FOLDED)) {
+      var deepestNode = lastNode;
+      while (true) {
+        if (deepestNode is YamlList &&
+            deepestNode.style == CollectionStyle.BLOCK &&
+            deepestNode.isNotEmpty) {
+          deepestNode = deepestNode.nodes.last;
+        } else if (deepestNode is YamlMap &&
+            deepestNode.style == CollectionStyle.BLOCK &&
+            deepestNode.isNotEmpty) {
+          deepestNode = deepestNode.nodes.values.last;
+        } else {
+          break;
+        }
+      }
+
+      if (deepestNode is YamlScalar &&
+          (deepestNode.style == ScalarStyle.LITERAL ||
+              deepestNode.style == ScalarStyle.FOLDED)) {
         while (nextNewLineIndex + 1 < yaml.length) {
           final nextLineEnd = yaml.indexOf('\n', nextNewLineIndex + 1);
           final lineSlice = nextLineEnd == -1

pkgs/yaml_edit/test/append_test.dart

diff --git a/pkgs/yaml_edit/test/append_test.dart b/pkgs/yaml_edit/test/append_test.dart
index fb43c47..f32eb56 100644
--- a/pkgs/yaml_edit/test/append_test.dart
+++ b/pkgs/yaml_edit/test/append_test.dart
@@ -261,6 +261,39 @@
       expect(doc.parseAt(['list', 1]).value, equals('next'));
     });
 
+    test('preserves multiple trailing newlines of nested |+ when appending',
+        () {
+      final doc = YamlEditor('list:\n  - map_key: |+\n      hello\n\n\n');
+      doc.appendToList(['list'], 'next');
+      final result = doc.toString();
+      expect(result,
+          equals('list:\n  - map_key: |+\n      hello\n\n\n  - next\n'));
+      expect(doc.parseAt(['list', 0, 'map_key']).value, equals('hello\n\n\n'));
+      expect(doc.parseAt(['list', 1]).value, equals('next'));
+    });
+
+    test(
+        'preserves multiple trailing newlines of nested list |+ when appending',
+        () {
+      final doc = YamlEditor('list:\n  - - |+\n      hello\n\n\n');
+      doc.appendToList(['list'], 'next');
+      final result = doc.toString();
+      expect(result, equals('list:\n  - - |+\n      hello\n\n\n  - next\n'));
+      expect(doc.parseAt(['list', 0, 0]).value, equals('hello\n\n\n'));
+      expect(doc.parseAt(['list', 1]).value, equals('next'));
+    });
+
+    test('preserves multiple trailing newlines of nested >+ when appending',
+        () {
+      final doc = YamlEditor('list:\n  - map_key: >+\n      hello\n\n\n');
+      doc.appendToList(['list'], 'next');
+      final result = doc.toString();
+      expect(result,
+          equals('list:\n  - map_key: >+\n      hello\n\n\n  - next\n'));
+      expect(doc.parseAt(['list', 0, 'map_key']).value, equals('hello\n\n\n'));
+      expect(doc.parseAt(['list', 1]).value, equals('next'));
+    });
+
     test('appends to list ending with single-line scalar without newlines', () {
       final doc = YamlEditor('list:\n  - item');
       doc.appendToList(['list'], 'item2');