How to reliably query payment status?

I have a lightning application that initiates payments using `xpay` over gRPC.
How can I reliably figure out the status of the payment.

## The problem with `listpays`

The problem is that `lispays` can transiently report `"failed"` while cln is still actively trying the payment. The status oscilates between `"pending"` and `"failed"` between individual route attempts.

We observed the issue on a lightning node and I created a [repro](https://github.com/ErikDeSmedt/lightning/tree/list-pays-bad-status) which yields the following results.

```
pending (x44) -> failed (x8) -> pending (x50) -> failed (x8) -> pending (x42) -> failed (x7) -> ... -> complete
```

A user who falsely believes that a payment has failed can run into danger.
- Eg: user tries another delivery method if lightning fails and end up paying twice
- Eg: when implementing swaps the user might revoke the incoming asset because the payment has failed

## The problem with waiting for a gRPC response

The `xpay` command returns once the payment is completed.
However, there is no guarantuee that we actually receive the response in case of network issues.

What should I do if this happens?
I don't want to call `listpays` because the payment might be marked as failed and end up succeeding.