Use covariant on SpanningWidget

@@ -6,6 +6,7 @@
 - Improve Text rendering
 - Add individual cell decoration
 - Improve Bullet Widget
+- Use covariant on SpanningWidget
 
 ## 3.2.0
 

@@ -67,11 +67,9 @@ class _FlexContext extends WidgetContext {
   int lastChild = 0;
 
   @override
-  void apply(WidgetContext other) {
-    if (other is _FlexContext) {
-      firstChild = other.firstChild;
-      lastChild = other.lastChild;
-    }
+  void apply(_FlexContext other) {
+    firstChild = other.firstChild;
+    lastChild = other.lastChild;
   }
 
   @override
@@ -504,10 +502,8 @@ class Flex extends MultiChildWidget implements SpanningWidget {
   bool get hasMoreWidgets => true;
 
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _FlexContext) {
-      _context.firstChild = context.lastChild;
-    }
+  void restoreContext(_FlexContext context) {
+    _context.firstChild = context.lastChild;
   }
 
   @override

@@ -32,13 +32,11 @@ class _GridViewContext extends WidgetContext {
   double? childMainAxis;
 
   @override
-  void apply(WidgetContext other) {
-    if (other is _GridViewContext) {
-      firstChild = other.firstChild;
-      lastChild = other.lastChild;
-      childCrossAxis = other.childCrossAxis;
-      childMainAxis = other.childMainAxis;
-    }
+  void apply(_GridViewContext other) {
+    firstChild = other.firstChild;
+    lastChild = other.lastChild;
+    childCrossAxis = other.childCrossAxis;
+    childMainAxis = other.childMainAxis;
   }
 
   @override
@@ -337,10 +335,8 @@ class GridView extends MultiChildWidget implements SpanningWidget {
   bool get hasMoreWidgets => true;
 
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _GridViewContext) {
-      _context.firstChild = context.lastChild;
-    }
+  void restoreContext(_GridViewContext context) {
+    _context.firstChild = context.lastChild;
   }
 
   @override

@@ -34,7 +34,7 @@ import 'widget.dart';
 abstract class WidgetContext {
   WidgetContext clone();
 
-  void apply(WidgetContext other);
+  void apply(covariant WidgetContext other);
 }
 
 abstract class SpanningWidget extends Widget {
@@ -48,7 +48,7 @@ abstract class SpanningWidget extends Widget {
 
   /// Aplpy the context for next layout
   @protected
-  void restoreContext(WidgetContext context);
+  void restoreContext(covariant WidgetContext context);
 }
 
 class NewPage extends Widget {

@@ -141,11 +141,9 @@ class _TableContext extends WidgetContext {
   int lastLine = 0;
 
   @override
-  void apply(WidgetContext other) {
-    if (other is _TableContext) {
-      firstLine = other.firstLine;
-      lastLine = other.lastLine;
-    }
+  void apply(_TableContext other) {
+    firstLine = other.firstLine;
+    lastLine = other.lastLine;
   }
 
   @override
@@ -425,7 +423,7 @@ class Table extends Widget implements SpanningWidget {
   }
 
   @override
-  void restoreContext(WidgetContext context) {
+  void restoreContext(_TableContext context) {
     _context.apply(context);
     _context.firstLine = _context.lastLine;
   }

@@ -50,11 +50,9 @@ class _WrapContext extends WidgetContext {
   int lastChild = 0;
 
   @override
-  void apply(WidgetContext other) {
-    if (other is _WrapContext) {
-      firstChild = other.firstChild;
-      lastChild = other.lastChild;
-    }
+  void apply(_WrapContext other) {
+    firstChild = other.firstChild;
+    lastChild = other.lastChild;
   }
 
   @override
@@ -394,10 +392,8 @@ class Wrap extends MultiChildWidget implements SpanningWidget {
   }
 
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _WrapContext) {
-      _context.firstChild = context.lastChild;
-    }
+  void restoreContext(_WrapContext context) {
+    _context.firstChild = context.lastChild;
   }
 
   @override