format dart files

formats all dart files using `dart format .` from the root project dir

this makes the code style repeatable by new contributors and makes PR review easier

lib/models/contact_group.dart

@@ -2,15 +2,9 @@ class ContactGroup {
   final String name;
   final List<String> memberKeys;
 
-  const ContactGroup({
-    required this.name,
-    required this.memberKeys,
-  });
+  const ContactGroup({required this.name, required this.memberKeys});
 
-  ContactGroup copyWith({
-    String? name,
-    List<String>? memberKeys,
-  }) {
+  ContactGroup copyWith({String? name, List<String>? memberKeys}) {
     return ContactGroup(
       name: name ?? this.name,
       memberKeys: memberKeys ?? List<String>.from(this.memberKeys),
@@ -18,16 +12,12 @@ class ContactGroup {
   }
 
   Map<String, dynamic> toJson() {
-    return {
-      'name': name,
-      'members': memberKeys,
-    };
+    return {'name': name, 'members': memberKeys};
   }
 
   factory ContactGroup.fromJson(Map<String, dynamic> json) {
-    final members = (json['members'] as List?)
-            ?.map((value) => value.toString())
-            .toList() ??
+    final members =
+        (json['members'] as List?)?.map((value) => value.toString()).toList() ??
         <String>[];
     return ContactGroup(
       name: json['name'] as String? ?? '',