Consume larger token notes first

[nventuro]

#7730 doesn't ask the oracle for the largest notes, and hence may require more iterations than strictly needed. It could be argued that we may not wish to return the notes in descending order as that may lead to excessive fragmentation and creation of change notes, but I'm not entirely sure how we may avoid it other than by having PXE be quite smart when it comes to note retrieval, or by passing extra hints to it.

If we do this, we should add a test to check that we're consuming the expected number of notes, as well as check that the extra constraints (for sorted notes) don't result in a large gate count increase (since we're not actually interested in those constraints in this case).