implemented backend wallet service connection

frontend/pweb/lib/models/wallet.dart

@@ -8,6 +8,7 @@ class Wallet {
   final double balance;
   final Currency currency;
   final bool isHidden;
+  final DateTime calculatedAt;
 
   Wallet({
     required this.id,
@@ -15,6 +16,7 @@ class Wallet {
     required this.name,
     required this.balance,
     required this.currency,
+    required this.calculatedAt,
     this.isHidden = true,
   });
 
@@ -25,14 +27,13 @@ class Wallet {
     Currency? currency,
     String? walletUserID,
     bool? isHidden,
-  }) {
-    return Wallet(
-      id: id ?? this.id,
-      name: name ?? this.name,
-      balance: balance ?? this.balance,
-      currency: currency ?? this.currency,
-      walletUserID: walletUserID ?? this.walletUserID,
-      isHidden: isHidden ?? this.isHidden,
-    );
-  }
+  }) => Wallet(
+    id: id ?? this.id,
+    name: name ?? this.name,
+    balance: balance ?? this.balance,
+    currency: currency ?? this.currency,
+    walletUserID: walletUserID ?? this.walletUserID,
+    isHidden: isHidden ?? this.isHidden,
+    calculatedAt: calculatedAt,
+  );
 }