Bucket classified votes into ISO-week buckets keyed by Monday's date.
Buckets are returned in chronological order (oldest first). Votes without
a valid sittingDate are bucketed under the empty-string key and placed at
the tail (sorting empty-string ahead of real dates would otherwise
distort week-over-week shift detection and baseline computations).
Bucket classified votes into ISO-week buckets keyed by Monday's date.
Buckets are returned in chronological order (oldest first). Votes without a valid sittingDate are bucketed under the empty-string key and placed at the tail (sorting empty-string ahead of real dates would otherwise distort week-over-week shift detection and baseline computations).