Generic fixes (#1304)

* fix mobx no element error

* fix mobx issue

* Remove unused code

* Enhance error handling for monero sync failure case

* Separate litecoin mnemonic exception from bitcoin

* - Enable onramper for polygon
- Add Kaspa validation

* Set null as the default length of address validation

* Modify EVM fee text [skip ci]

* Add seed length option to polygon

* Add digibyte

* Update configure_cake_wallet.sh and fix conflicts

* Pin bottom section

* Fix Solana missing isTestnet param

lib/core/address_validator.dart

@@ -257,9 +257,9 @@ class AddressValidator extends TextValidator {
       case CryptoCurrency.near:
         return [64];
       case CryptoCurrency.btcln:
-        return null;
+      case CryptoCurrency.kaspa:
       default:
-        return [];
+        return null;
     }
   }