adding missing const

frontend/lib/pages/new_trip_preferences.dart

@@ -10,7 +10,7 @@ import 'package:flutter/material.dart';
 
 class NewTripPreferencesPage extends StatefulWidget {
   final Trip trip;
-  const NewTripPreferencesPage({required this.trip});
+  const NewTripPreferencesPage({super.key, required this.trip});
 
   @override
   _NewTripPreferencesPageState createState() => _NewTripPreferencesPageState();
@@ -34,14 +34,14 @@ class _NewTripPreferencesPageState extends State<NewTripPreferencesPage> with Sc
       child: Scaffold(
         body: ListView(
           children: [
-          Center(
+          const Center(
             child: Padding(
             padding: EdgeInsets.only(left: 10, right: 10, top: 20, bottom: 0),
               child: Text('Tell us about your ideal trip.', style: TextStyle(fontSize: 18))
             ),
           ),
 
-          Divider(indent: 25, endIndent: 25, height: 50),
+          const Divider(indent: 25, endIndent: 25, height: 50),
 
           durationPicker(preferences.maxTime),
 
@@ -78,7 +78,7 @@ class _NewTripPreferencesPageState extends State<NewTripPreferencesPage> with Sc
         title: Text(preferences.maxTime.description),
         subtitle: CupertinoTimerPicker(
           mode: CupertinoTimerPickerMode.hm,
-          initialTimerDuration: Duration(minutes: 90),
+          initialTimerDuration: const Duration(minutes: 90),
           minuteInterval: 15,
           onTimerDurationChanged: (Duration newDuration) {
             setState(() {