Tiltify campaign ID whose trains to poll + merge.
Live donation firehose to feed into the process-donations
matcher. When the array changes reference, the merger POSTs and
folds the returned trains into local state.
OptionalisWhether the caller is a dashboard (default false). Dashboards
want the full train history; on-stream overlays pass
allowEnded=false + filterInvalid=true to the underlying
fetcher.
Params for useDonationTrainState.