This makes `LNWallet.pay_to_node()` wait
`PaySession.TIMEOUT_WAIT_FOR_NEXT_RESOLVED_HTLC` (0.5 sec) for another
htlc to get resolved after receiving a htlc failure during a payment
attempt.
This seems to make payments more reliable in scenarios where we receive
multiple htlc failures closely after each other as
`create_route_for_payment` then has access to the failed routes/failure
information of all these htlcs when trying to re-split the outstanding
amount.
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