Add entity for `OneTimePayment`

[lordshashank]

Currently subgraph doesn't tracks one time payment at all and not even considers it as settlement. A part of it get resolved by #86 , but still there is no robust way to get the total amount settled by rail, provider, etc in a time bound way or with other filters. This can help in creating monthly leaderboards, make analytics on actual distribution of fee on different parameters, etc if needed.

Discussion: https://filecoinproject.slack.com/archives/C07CGTXHHT4/p1769442668077879

[pyropy]

Are you saying that one-time payments should be counted towards settlements? In my opinion one-time payments and settlements are separate things and should not be mixed. However, I agree that they should be tracked as without it there's no way of knowing correct account or payment rail balance.

[lordshashank]

hmm, I think they are settlements as they are part of rail lockups, etc and should be counted as "total usdfc settled" in any dashboard as that amount goes through filecoin pay, 0.5% fee is extracted and is in settlement volume. even in case of filcdn it is "egress settlement"