adding missing const

frontend/lib/modules/landmark_card.dart

@@ -13,12 +13,12 @@ import 'package:anyway/structs/landmark.dart';
 class LandmarkCard extends StatefulWidget {
   final Landmark landmark;
   final Trip parentTrip;
-  
-  LandmarkCard(
+
+  const LandmarkCard(
     this.landmark,
     this.parentTrip,
   );
-  
+
   @override
   _LandmarkCardState createState() => _LandmarkCardState();
 }
@@ -26,7 +26,7 @@ class LandmarkCard extends StatefulWidget {
 
 class _LandmarkCardState extends State<LandmarkCard> {
   @override
-  Widget build(BuildContext context) {      
+  Widget build(BuildContext context) {
     return Container(
       constraints: BoxConstraints(
         // express the max height in terms text lines
@@ -38,7 +38,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
         ),
         elevation: 5,
         clipBehavior: Clip.antiAliasWithSaveLayer,
-        
+
         // if the image is available, display it on the left side of the card, otherwise only display the text
         child: Row(
           crossAxisAlignment: CrossAxisAlignment.start,
@@ -66,11 +66,11 @@ class _LandmarkCardState extends State<LandmarkCard> {
                       color: PRIMARY_COLOR,
                       child: Center(
                         child: Padding(
-                          padding: EdgeInsets.all(5),
+                          padding: const EdgeInsets.all(5),
                           child: Row(
                             mainAxisAlignment: MainAxisAlignment.center,
                             children: [
-                              Icon(Icons.timer_outlined, size: 16),
+                              const Icon(Icons.timer_outlined, size: 16),
                               Text("${widget.landmark.duration?.inMinutes} minutes"),
                             ],
                           )
@@ -97,7 +97,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
                           overflow: TextOverflow.ellipsis,
                           maxLines: 2,
                         ),
-                          
+
                         if (widget.landmark.nameEN != null)
                           Text(
                             widget.landmark.nameEN!,
@@ -114,7 +114,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
 
                   SingleChildScrollView(
                     scrollDirection: Axis.horizontal,
-                    padding: EdgeInsets.only(left: 5, right: 5, bottom: 10),
+                    padding: const EdgeInsets.only(left: 5, right: 5, bottom: 10),
                     // the scroll view should be flush once the buttons are scrolled to the left
                     // but initially there should be some padding
                     child: Wrap(
@@ -124,7 +124,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
                         doneToggleButton(),
                         if (widget.landmark.websiteURL != null)
                           websiteButton(),
-                        
+
                         optionsButton()
                       ],
                     ),
@@ -181,7 +181,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
           title: const Text('Favorite'),
           onTap: () async {
             rootScaffoldMessengerKey.currentState!.showSnackBar(
-              SnackBar(content: Text("Not implemented yet"))
+              const SnackBar(content: Text("Not implemented yet"))
             );
           },
         ),
@@ -193,7 +193,7 @@ class _LandmarkCardState extends State<LandmarkCard> {
 
 
 Widget imagePlaceholder (Landmark landmark) => Expanded(
-  child: 
+  child:
   Container(
     decoration: const BoxDecoration(
       gradient: LinearGradient(