Changed argument of function NewBatcher from LoopOutFetcher to SweepFetcher
(returning new public type SweepInfo).
This change is backwards-incompatible on the package layer, but nobody seems
to use the package outside of Loop.
To use NewBatcher inside Loop, turn loopdb into SweepFetcher using
function NewSweepFetcherFromSwapStore.
It used to be set to default (defaultBatchConfTarget = 12) which
could in theory affect fee rate if updateRbfRate() and publish()
were not called before the batch was saved. (Unlikely scenario.)
Method sweepbatcher.Store.FetchBatchSweeps (implementation using real DB) runs
JOIN query to load LoopOut from swaps table. Now the mock does the same.
It is needed to test store and load scenarios in tests.
If the sweep was successfully updated in the batch, no need to
try to add it to all other batches.
Added a test reproducing adding a sweep to both batches without this change.
Previously we'd report the fees per sweep as the total sweep cost of a
batch. With this change the reported cost will be the proportional fee
which should be equal for all sweeps except if there's any rounding
difference in which case that is paid by the sweep belonging to the
first input of the batch tx.