Support rejecting duplicate offer payments

[TheBlueMatt]

When using BOLT 12 to receive payments which are "single-use" (eg generating a unique offer for a merchant who wants to receive payment for an order once) ldk-node should support looking up the OfferId from the PaymentClaimable event and rejecting duplicate payments for an offer marked single-use, just like we can for BOLT 11 payments which are redundant.

[tnull]

To do this properly (read: without having to iterate through all payments in the store), we probably want to wait until after #425.

[TheBlueMatt]

I don't think there's a particular rush for this in the slightest. Anyone doing single-use invoices for quite a while is going to be using BOLT 11