Find All People With Secret

Given timestamped pairwise meetings and that person 0 initially shares a secret with firstPerson at time 0, determine who knows the secret after all meetings, where meetings at the same time allow instantaneous multi-hop sharing. The core challenge is to process meetings in time order and, for each timestamp, propagate the secret across the subgraph of simultaneous attendees (e.g., via union-find or BFS) to account for chained transmissions.