Winner of one ranking criterion — just the criterion and the
winning point's report. Everything else lives on the report and is
never duplicated here: the trades in report.tradesList; the
author track lives deduplicated in the bucket's tracks[].
criterion: SweepRankingCriterion
The ranking criterion this winner belongs to.
report: ISweepPointReport
Winning point report; null when the bucket produced no reports.