feat: add pastParticipants support in history sync

Surfaces past group participant data from WhatsApp history sync messages.
Previously pastParticipants was dropped during event buffering because
it was overwritten instead of accumulated across chunks.

- src/Types/Events.ts: add pastParticipants to BaileysEventMap['messaging-history.set'] and BufferedEventData.historySets
- src/Utils/event-buffer.ts: accumulate pastParticipants via spread array instead of overwriting; include in consolidateEvents output
- src/Utils/history.ts: pass item.pastParticipants in processHistoryMessage return

Refs: WhiskeySockets/Baileys#2426

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Types/Events.ts

@@ -27,6 +27,7 @@ export type BaileysEventMap = {
 		chats: Chat[]
 		contacts: Contact[]
 		messages: WAMessage[]
+		pastParticipants?: proto.IPastParticipants[] | null
 		isLatest?: boolean
 		progress?: number | null
 		syncType?: proto.HistorySync.HistorySyncType | null
@@ -185,6 +186,7 @@ export type BufferedEventData = {
 		chats: { [jid: string]: Chat }
 		contacts: { [jid: string]: Contact }
 		messages: { [uqId: string]: WAMessage }
+		pastParticipants?: proto.IPastParticipants[]
 		empty: boolean
 		isLatest: boolean
 		progress?: number | null

src/Utils/event-buffer.ts

@@ -967,6 +967,10 @@ function append<E extends BufferableEvent>(
 				}
 			}
 
+			data.historySets.pastParticipants = [
+				...(data.historySets.pastParticipants || []),
+				...(eventData.pastParticipants || [])
+			]
 			data.historySets.empty = false
 			data.historySets.syncType = eventData.syncType
 			data.historySets.progress = eventData.progress
@@ -1292,6 +1296,7 @@ function consolidateEvents(data: BufferedEventData) {
 			chats: Object.values(data.historySets.chats),
 			messages: Object.values(data.historySets.messages),
 			contacts: Object.values(data.historySets.contacts),
+			pastParticipants: data.historySets.pastParticipants,
 			syncType: data.historySets.syncType,
 			progress: data.historySets.progress,
 			isLatest: data.historySets.isLatest,

src/Utils/history.ts

@@ -378,6 +378,7 @@ export const processHistoryMessage = (item: proto.IHistorySync, logger?: ILogger
 		chats,
 		contacts,
 		messages,
+		pastParticipants: item.pastParticipants,
 		lidPnMappings,
 		syncType: item.syncType,
 		progress: item.progress