consider adding a reject message for PFI to send to Alice

[jiyoonie9]

when PFI needs to close a tbdex exchange before an order goes through, it currently sends a Close message, which has the success field in it, a boolean.

However, in the scenario where PFI sends a Close after sending a Quote, it's unclear what success: false means in this scenario. At this point in the exchange, no "true" exchange of assets has occurred, so it's weird to say an exchange was not successful.

Instead, for all the times when PFI needs to close the exchange before the actual money movements have happened, they should send another message, maybe named Reject, to indicate that no money movement has happened, but PFI is declining to move further in the exchange.