better linting

lib/features/core/widgets/gap.dart

@@ -1,8 +1,12 @@
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
+/// Const evenly-sized gap.
 class Gap extends LeafRenderObjectWidget {
-  const Gap(this.size, {Key? key}) : super(key: key);
+  const Gap(
+    this.size, {
+    super.key,
+  });
 
   final double size;
 
@@ -58,13 +62,14 @@ class RenderGap extends RenderBox {
   }
 }
 
+/// Animates [Gap] insertion.
 class AnimatedGap extends StatefulWidget {
   const AnimatedGap(
     this.gap, {
-    Key? key,
     this.duration = const Duration(milliseconds: 200),
     this.curve = Curves.easeInOut,
-  }) : super(key: key);
+    super.key,
+  });
 
   final Duration duration;
   final double gap;
@@ -107,10 +112,10 @@ class _AnimatedGapState extends State<AnimatedGap> with SingleTickerProviderStat
 class AnimatedSliverGap extends StatefulWidget {
   const AnimatedSliverGap(
     this.gap, {
-    Key? key,
     this.duration = const Duration(milliseconds: 200),
     this.curve = Curves.easeInOut,
-  }) : super(key: key);
+    super.key,
+  });
 
   final Duration duration;
   final double gap;

lib/features/core/widgets/state/multi_value_listenable_builder.dart

@@ -8,10 +8,13 @@ class MultiValueListenableBuilder extends StatelessWidget {
     required this.builder,
     this.child,
     super.key,
-  }) : assert(valueListenables.length != 0);
+  }) : assert(
+          valueListenables.length != 0,
+          'Attached valueListenables must not be empty',
+        );
 
   /// List of [ValueListenable]s to be listened to.
-  final List<ValueListenable> valueListenables;
+  final List<ValueListenable<dynamic>> valueListenables;
 
   /// The builder function to be called when value of any of the [ValueListenable] changes.
   /// The order of values list will be same as [valueListenables] list.