For nodes with many channels this is a tremendous improvement in pay
performance. PR #7611 improves payment performance from 15 seconds to
13.5 seconds on one of our nodes. This commit improves payment
performance from 13.5 seconds to 5.7 seconds.
Changelog-Fixed: Improved pathfinding speed for large nodes.
This minimizes the need to convert back and forth from and to sat
values, and it also removes a new instance of sats in the public
interface (`channel_hints`).
Suggested-By: Rusty Russell <@rustyrussell>