CW-1103:Token Validation Issues (#2327)

* feat(token_validation): Improve flow for adding new tokens across wallets

This change:
- Implements check to see if a token is already added, preventing duplicates
- Triggers dialog warning if its a duplicate token
- Takes EVM Chains contract adddress case-insensitivity when making checks for potential scams.

* 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.

* Update lib/src/screens/dashboard/edit_token_page.dart

---------

Co-authored-by: Omar Hatem <omarh.ismail1@gmail.com>

lib/ethereum/cw_ethereum.dart

@@ -199,8 +199,16 @@ class CWEthereum extends Ethereum {
   }
 
   @override
-  List<String> getDefaultTokenContractAddresses() =>
-      DefaultEthereumErc20Tokens().initialErc20Tokens.map((e) => e.contractAddress).toList();
+  List<String> getDefaultTokenContractAddresses() {
+    return DefaultEthereumErc20Tokens().initialErc20Tokens.map((e) => e.contractAddress).toList();
+  }
+
+
+  @override
+  bool isTokenAlreadyAdded(WalletBase wallet, String contractAddress) {
+    final ethereumWallet = wallet as EthereumWallet;
+    return ethereumWallet.erc20Currencies.any((element) => element.contractAddress.toLowerCase() == contractAddress.toLowerCase());
+  }
 
   Future<PendingTransaction> createTokenApproval(WalletBase wallet, BigInt amount, String spender,
           CryptoCurrency token, TransactionPriority priority) =>