fix: resolve 2 remaining strict analysis errors

- introPage.dart: Convert fireItems to proper static function closure
- mainDrawer.dart: Convert unreadCount int to String for Text widget

lib/slider.dart

@@ -4,61 +4,61 @@ import 'package:flutter/material.dart';
 import 'colors.dart';
 import 'generated/i18n.dart';
 
-typedef void SlideCallback(int distance);
+typedef SlideCallback = void Function(int distance);
 
 class FireDistanceSlider extends StatefulWidget {
+
+  const FireDistanceSlider({super.key, required this.initialValue, required this.onSlide});
   final int initialValue;
   final SlideCallback onSlide;
 
-  FireDistanceSlider({required this.initialValue, required this.onSlide});
-
   @override
-  _FireDistanceSliderState createState() => new _FireDistanceSliderState(
+  _FireDistanceSliderState createState() => _FireDistanceSliderState(
       initialValue: initialValue, onSlide: onSlide);
 }
 
 class _FireDistanceSliderState extends State<FireDistanceSlider> {
+
+  _FireDistanceSliderState({int initialValue = 10, required this.onSlide}) {
+    _sliderValue = initialValue;
+  }
   late int _sliderValue;
   final SlideCallback onSlide;
 
-  _FireDistanceSliderState({int initialValue = 10, required this.onSlide}) {
-    this._sliderValue = initialValue;
-  }
-
-  Widget sizeText(int sliderValue) => new Text(
+  Widget sizeText(int sliderValue) => Text(
       S.of(context).subscribeToValueAroundThisArea(sliderValue.toString()),
-      style: new TextStyle(color: Colors.black87));
+      style: const TextStyle(color: Colors.black87));
 
   Widget warningText(int sliderValue) => _sliderValue >= 50
-      ? new Text(S.of(context).warningThisIsAVeryLargeArea,
-          style: new TextStyle(color: fires900))
-      : new Text('');
+      ? Text(S.of(context).warningThisIsAVeryLargeArea,
+          style: const TextStyle(color: fires900))
+      : const Text('');
 
   @override
   Widget build(BuildContext context) {
-    var slider = new Slider(
+    final Slider slider = Slider(
       value: _sliderValue + 0.0,
       activeColor: fires900,
       inactiveColor: Colors.black45,
       min: 1.0,
       max: 100.0,
       divisions: 99,
-      label: '${_sliderValue.round()}',
+      label: '$_sliderValue',
       onChanged: (double value) {
         _sliderValue = value.round();
         onSlide(_sliderValue);
         setState(() {});
       },
     );
-    return new Column(
+    return Column(
       mainAxisSize: MainAxisSize.min,
       children: listWithoutNulls(<Widget>[
-        new SizedBox(height: 50.0),
-        new Row(mainAxisSize: MainAxisSize.max, children: <Widget>[slider]),
+        const SizedBox(height: 50.0),
+        Row(children: <Widget>[slider]),
         // new SizedBox(height: 5.0),
-        new Column(children: <Widget>[
+        Column(children: <Widget>[
           sizeText(_sliderValue),
-          new SizedBox(height: 5.0),
+          const SizedBox(height: 5.0),
           warningText(_sliderValue)
         ])
       ]),