Fix hr tag ignoring custom builders and paddingBuilders

lib/src/builder.dart

@@ -474,7 +474,16 @@ class MarkdownBuilder implements md.NodeVisitor {
           child: child,
         );
       } else if (tag == 'hr') {
-        child = Container(decoration: styleSheet.horizontalRuleDecoration);
+        if (!builders.containsKey(tag)) {
+          child = Container(decoration: styleSheet.horizontalRuleDecoration);
+        }
+      }
+
+      if (tag == 'hr' && paddingBuilders.containsKey(tag)) {
+        child = Padding(
+          padding: paddingBuilders[tag]!.getPadding(),
+          child: child,
+        );
       }
 
       _addBlockChild(child);

test/horizontal_rule_test.dart

@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
 import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:markdown/markdown.dart' as md;
 import 'utils.dart';
 
 void main() => defineTests();
@@ -84,5 +85,68 @@ void defineTests() {
         ]);
       },
     );
+    testWidgets(
+      'custom builder for hr is respected',
+      (WidgetTester tester) async {
+        const String data = '---';
+        await tester.pumpWidget(
+          boilerplate(
+            MarkdownBody(
+              data: data,
+              builders: <String, MarkdownElementBuilder>{
+                'hr': _CustomHrBuilder(),
+              },
+            ),
+          ),
+        );
+
+        expect(find.byType(ColoredBox), findsOneWidget);
+        final ColoredBox box = tester.widget(find.byType(ColoredBox));
+        expect(box.color, Colors.red);
+      },
+    );
+
+    testWidgets(
+      'paddingBuilders for hr is applied',
+      (WidgetTester tester) async {
+        const String data = '---';
+        const double paddingX = 16.0;
+        await tester.pumpWidget(
+          boilerplate(
+            MarkdownBody(
+              data: data,
+              paddingBuilders: <String, MarkdownPaddingBuilder>{
+                'hr': _CustomPaddingBuilder(paddingX),
+              },
+            ),
+          ),
+        );
+
+        final Finder paddingFinder = find.byType(Padding);
+        final List<Padding> paddings = tester.widgetList<Padding>(paddingFinder).toList();
+        final bool hasHrPadding = paddings.any(
+          (Padding p) => p.padding.along(Axis.horizontal) == paddingX * 2,
+        );
+        expect(hasHrPadding, isTrue);
+      },
+    );
   });
 }
+
+class _CustomHrBuilder extends MarkdownElementBuilder {
+  @override
+  Widget visitElementAfter(md.Element element, TextStyle? preferredStyle) {
+    return const ColoredBox(color: Colors.red, child: SizedBox(height: 2, width: double.infinity));
+  }
+}
+
+class _CustomPaddingBuilder extends MarkdownPaddingBuilder {
+  _CustomPaddingBuilder(this.paddingX);
+
+  final double paddingX;
+
+  @override
+  EdgeInsets getPadding() {
+    return EdgeInsets.symmetric(horizontal: paddingX);
+  }
+}