Update many checklist cells

Set one status on up to 500 intersections at once — a whole column, a row or any set — each with its expectedUpdatedAt from the last read (null when untouched). The status is todo, in_progress, done or the key of one of the organisation’s own statuses (checklist_list_statuses). Cells are never overwritten blindly: one changed by somebody since your read (stale), already at that status (unchanged), not in this checklist (not_found) or a document item without accessible evidence for done (needs_document) is left as it was and listed in skipped with its reason; the others are written. The participants get one notice for the whole batch.