refactor(token_validation): Modify token management flow

This change:
- Removes duplicate token check during token addition in EVMChainWalletBase.
- Introduces a flag to indicate if a token is being edited
- Adjusts token addition validation to bypass checks when editing an existing token.

cw_evm/lib/evm_chain_wallet.dart

@@ -664,11 +664,6 @@ abstract class EVMChainWalletBase
   List<Erc20Token> get erc20Currencies => evmChainErc20TokensBox.values.toList();
 
   Future<void> addErc20Token(Erc20Token token) async {
-    if (evmChainErc20TokensBox.values.any((element) =>
-        element.contractAddress.toLowerCase() == token.contractAddress.toLowerCase())) {
-      throw Exception('Token already exists');
-    }
-
     String? iconPath;
 
     if ((token.iconPath == null || token.iconPath!.isEmpty) && !token.isPotentialScam) {

lib/src/screens/dashboard/edit_token_page.dart

@@ -73,6 +73,7 @@ class _EditTokenPageBodyState extends State<EditTokenPageBody> {
 
   bool _showDisclaimer = false;
   bool _disclaimerChecked = false;
+  bool isEditingToken = false;
 
   @override
   void initState() {
@@ -88,11 +89,15 @@ class _EditTokenPageBodyState extends State<EditTokenPageBody> {
       _tokenSymbolController.text = widget.token!.title;
       _tokenDecimalController.text = widget.token!.decimals.toString();
       _tokenIconPathController.text = widget.token?.iconPath ?? '';
+
+      isEditingToken = true;
     }
 
     if (widget.initialContractAddress != null) {
       _contractAddressController.text = widget.initialContractAddress!;
       _getTokenInfo();
+
+      isEditingToken = true;
     }
 
     _contractAddressFocusNode.addListener(() {
@@ -200,7 +205,9 @@ class _EditTokenPageBodyState extends State<EditTokenPageBody> {
                         onPressed: () async {
                           if (_formKey.currentState!.validate() &&
                               (!_showDisclaimer || _disclaimerChecked)) {
-                            final isTokenAlreadyAdded = await widget.homeSettingsViewModel
+                            final isTokenAlreadyAdded = isEditingToken
+                                ? false
+                                : await widget.homeSettingsViewModel
                                     .checkIfTokenIsAlreadyAdded(_contractAddressController.text);
                             if (isTokenAlreadyAdded) {
                               showPopUp<void>(

lib/view_model/dashboard/home_settings_view_model.dart

@@ -127,7 +127,7 @@ abstract class HomeSettingsViewModelBase with Store {
   }
 
   @action
-  Future<bool> checkIfTokenIsAlreadyAdded(String contractAddress) async {
+  bool checkIfTokenIsAlreadyAdded(String contractAddress) {
     if (_balanceViewModel.wallet.type == WalletType.ethereum) {
       return ethereum!.isTokenAlreadyAdded(_balanceViewModel.wallet, contractAddress);
     }