No sign in csv export

[markdavidjohnson]

Description:
When exporting CSVs from the All Activities view, there is currently no difference in the sign of amounts for received vs sent. This can be confusing for users when analyzing their transaction data.

File:
lib/bloc/csv_exporter.dart

Issue:
This line is responsible for adding the amount to the CSV export without differentiating the signs for received or sent transactions:
paymentItem.add(paymentInfo.amount.toString());

Suggested Fix:
Modify the line to assign the correct sign to the amount based on whether it's a received or sent transaction:
paymentItem.add(((paymentInfo.type == PaymentType.SENT || paymentInfo.type == PaymentType.WITHDRAWAL ? -1 : 1) * paymentInfo.amount).toString());

This change will apply a negative sign to sent and withdrawal transactions, making it easier for users to analyze their transaction data.

[tlindi]

+1 for this.

Also verify similar for fees too, please.