[XMR] "Bug": Transaction constructor for sending payment combines more utxos than needed
If you want to send frequent transactions in a row, you need to have more than 1 output, because in each transaction all the input utxos are locked until it's confirmed.

Because of this, it's good to create more outputs for yourself (send fractions to different subaddresses).

BUT the problem is that when sending a transaction, wallet seems to cycle through all utxos and use more utxos than are actually needed. I found the code in https://github.com/cake-tech/cake_wallet/blob/main/cw_monero/lib/monero_wallet.dart#L205
```dart
for (final utx in unspentCoins) {
      if (utx.isSending) {
        allInputsAmount += utx.value;
        inputs.add(utx.keyImage!);
      }
    }
```

I'm not that familiar with the whole codebase, but it seems like the issue lies here.

I propose some check for the amount required and stop adding new input utxos after that is reached.
```dart
final amountToSend = <get_it_from_somewhere>;
for (final utx in unspentCoins) {
      if (utx.isSending && (allInputsAmount < amountToSend)) {
        allInputsAmount += utx.value;
        inputs.add(utx.keyImage!);
      }
    }
```

Fixing this is a crucial for the UX of this app, because if it merges your previously divided outputs into one, it fights against your effort. Thanks