Ideation: Emergency refund of user lockups via presigned transations

[kilrau]

Since we have some funds locked in swap addresses probably forever either due to loss of refund data OR just out of oversight (funds weren't claimed and users never bothered to take care of it) @michael1011 and I just came up with the idea of swap clients waiting for the lockup transaction to happen and then creating presigned transaction(s) refunding the swap back to the input address(es) with a timelock of e.g. 14 days, sign the transactions and send them to a new boltz endpoint.

Like this Boltz could "return funds to sender" after the timelock without ever taking custody. Major problem is that we can't be sure the input addresses are under users control (exchanges etc) and especially if lockup transactions have multiple (potentially hundreds of inputs). Then the swap client would need to create a presigned refund tx for each of them and rely on the user contacting Boltz to tell us which to broadcast. Creating these transactions will be resource intensive in a browser, especially with hundreds. This is not pretty and definitely just an idea for now but I'd absolutely love to avoid having funds stuck forever in Boltz lockup addresses.