feat(flutter_sanity_portable_text): support scoped PortableTextConfig per block

packages/sanity/flutter_sanity_portable_text/lib/ui/portable_text_block.dart

@@ -14,11 +14,18 @@ class PortableTextBlock extends StatelessWidget {
   /// The model representing the block of Portable Text.
   final TextBlockItem model;
 
-  const PortableTextBlock({super.key, required this.model});
+  /// Optional configuration override for this block.
+  ///
+  /// When null, falls back to [PortableTextConfig.shared].
+  /// Use [PortableTextConfig.copyWith] to create a scoped config with
+  /// overrides (e.g. custom [PortableTextConfig.itemPadding]).
+  final PortableTextConfig? config;
+
+  const PortableTextBlock({super.key, required this.model, this.config});
 
   @override
   Widget build(final BuildContext context) {
-    final config = PortableTextConfig.shared;
+    final config = this.config ?? PortableTextConfig.shared;
 
     final spans = model.children
         .map((final span) => _buildInlineSpan(span, Theme.of(context), context))

packages/sanity/flutter_sanity_portable_text/lib/ui/portable_text_config.dart

@@ -73,6 +73,31 @@ final class PortableTextConfig {
 
   PortableTextConfig._();
 
+  /// Creates a copy of this [PortableTextConfig] but with the given fields
+  /// replaced with new values.
+  ///
+  /// This is useful when you need a scoped configuration for a specific
+  /// [PortableTextBlock] without mutating the global [shared] instance.
+  /// For example, rendering blocks inside a [Row] where the default
+  /// [itemPadding] would throw off cross-axis alignment.
+  PortableTextConfig copyWith({
+    EdgeInsets? itemPadding,
+    double? listIndent,
+    BulletRenderer? bulletRenderer,
+    TextStyle? Function(BuildContext)? baseStyle,
+  }) {
+    final copy = PortableTextConfig._();
+    copy.styles.addAll(styles);
+    copy.blocks.addAll(blocks);
+    copy.blockContainers.addAll(blockContainers);
+    copy.markDefs.addAll(markDefs);
+    copy.baseStyle = baseStyle ?? this.baseStyle;
+    copy.bulletRenderer = bulletRenderer ?? this.bulletRenderer;
+    copy.itemPadding = itemPadding ?? this.itemPadding;
+    copy.listIndent = listIndent ?? this.listIndent;
+    return copy;
+  }
+
   /// Applies the custom configuration to the shared instance of the [PortableTextConfig].
   void apply({
     final double listIndent = defaultListIndent,

packages/sanity/flutter_sanity_portable_text/test/scoped_config_test.dart

@@ -0,0 +1,139 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_sanity_portable_text/flutter_sanity_portable_text.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  setUp(() {
+    PortableTextConfig.shared.reset();
+  });
+
+  group('PortableTextConfig.copyWith', () {
+    test('copies all values from source by default', () {
+      PortableTextConfig.shared.apply(
+        itemPadding: const EdgeInsets.all(16),
+        listIndent: 32,
+      );
+
+      final scoped = PortableTextConfig.shared.copyWith();
+
+      expect(scoped.itemPadding, const EdgeInsets.all(16));
+      expect(scoped.listIndent, 32);
+      expect(scoped.styles.keys, PortableTextConfig.shared.styles.keys);
+      expect(scoped.blocks.keys, PortableTextConfig.shared.blocks.keys);
+      expect(scoped.blockContainers.keys,
+          PortableTextConfig.shared.blockContainers.keys);
+    });
+
+    test('overrides itemPadding when specified', () {
+      PortableTextConfig.shared.apply(
+        itemPadding: const EdgeInsets.only(bottom: 8),
+      );
+
+      final scoped = PortableTextConfig.shared.copyWith(
+        itemPadding: EdgeInsets.zero,
+      );
+
+      expect(scoped.itemPadding, EdgeInsets.zero);
+      expect(PortableTextConfig.shared.itemPadding,
+          const EdgeInsets.only(bottom: 8));
+    });
+
+    test('overrides listIndent when specified', () {
+      final scoped = PortableTextConfig.shared.copyWith(
+        listIndent: 40,
+      );
+
+      expect(scoped.listIndent, 40);
+      expect(PortableTextConfig.shared.listIndent,
+          PortableTextConfig.defaultListIndent);
+    });
+
+    test('does not mutate the source config', () {
+      final original = PortableTextConfig.shared;
+      final originalPadding = original.itemPadding;
+      final originalIndent = original.listIndent;
+
+      original.copyWith(
+        itemPadding: const EdgeInsets.all(99),
+        listIndent: 99,
+      );
+
+      expect(original.itemPadding, originalPadding);
+      expect(original.listIndent, originalIndent);
+    });
+  });
+
+  group('PortableTextBlock with scoped config', () {
+    testWidgets('uses scoped config itemPadding instead of shared',
+        (WidgetTester tester) async {
+      PortableTextConfig.shared.itemPadding = const EdgeInsets.only(bottom: 10);
+
+      final scoped = PortableTextConfig.shared.copyWith(
+        itemPadding: EdgeInsets.zero,
+      );
+
+      final block = TextBlockItem(children: [
+        Span(text: 'Hello, World'),
+      ]);
+
+      await tester.pumpWidget(MaterialApp(
+        home: PortableTextBlock(model: block, config: scoped),
+      ));
+
+      final padding = tester.widget<Padding>(find.byType(Padding));
+      expect(padding.padding, EdgeInsets.zero);
+    });
+
+    testWidgets('falls back to shared config when no scoped config is provided',
+        (WidgetTester tester) async {
+      PortableTextConfig.shared.itemPadding = const EdgeInsets.only(bottom: 12);
+
+      final block = TextBlockItem(children: [
+        Span(text: 'Hello, World'),
+      ]);
+
+      await tester.pumpWidget(MaterialApp(
+        home: PortableTextBlock(model: block),
+      ));
+
+      final padding = tester.widget<Padding>(find.byType(Padding));
+      expect(padding.padding, const EdgeInsets.only(bottom: 12));
+    });
+
+    testWidgets(
+        'scoped config with zero padding in Row enables correct center alignment',
+        (WidgetTester tester) async {
+      final scoped = PortableTextConfig.shared.copyWith(
+        itemPadding: EdgeInsets.zero,
+      );
+
+      final block = TextBlockItem(children: [
+        Span(text: 'Hello, World'),
+      ]);
+
+      await tester.pumpWidget(MaterialApp(
+        home: Row(
+          crossAxisAlignment: CrossAxisAlignment.center,
+          children: [
+            const Icon(Icons.star, size: 32),
+            const SizedBox(width: 16),
+            Expanded(
+              child: PortableTextBlock(model: block, config: scoped),
+            ),
+          ],
+        ),
+      ));
+
+      // Verify the block's padding is zero — no trailing space to
+      // throw off the Row's cross-axis center alignment.
+      final padding = tester.widget<Padding>(find.byType(Padding));
+      expect(padding.padding, EdgeInsets.zero);
+
+      // Verify the icon and text are vertically centered in the Row.
+      final iconCenter = tester.getCenter(find.byIcon(Icons.star));
+      final textCenter =
+          tester.getCenter(find.text('Hello, World', findRichText: true));
+      expect(iconCenter.dy, textCenter.dy);
+    });
+  });
+}