feat: add inbound username support and USync username protocol (#382)

* feat: add inbound username support and USync username protocol

Aligns with Baileys upstream PR #2480. WhatsApp is rolling out an
inbound username field that maps to the user's LID. This change is
purely additive — it captures and propagates the new optional field
through types, decoders, USync queries, and group/contact events.

Skipped intentionally to preserve InfiniteAPI's LID/PN customization:
- handleGroupNotification in messages-recv.ts (custom LID->PN flow on
  groups.upsert / participants.map). Username for these specific
  events still flows via process-message's emitParticipantsUpdate
  (reads message.key.participantUsername added in decode-wa-message).

Carousel/buttons code (messages.ts, messages-send.ts) untouched.

Co-Authored-By: Renato Alcara

src/Socket/messages-recv.ts

@@ -2223,6 +2223,7 @@ export const makeMessagesRecvSocket = (config: SocketConfig) => {
 							fromMe,
 							participant: node.attrs.participant,
 							participantAlt,
+							participantUsername: node.attrs.participant_username,
 							addressingMode,
 							id: node.attrs.id,
 							...(msg.key || {})
@@ -2231,6 +2232,10 @@ export const makeMessagesRecvSocket = (config: SocketConfig) => {
 						msg.messageTimestamp = +node.attrs.t!
 
 						const fullMsg = proto.WebMessageInfo.fromObject(msg) as WAMessage
+						// Preserve custom WAMessageKey fields (participantAlt, participantUsername,
+						// addressingMode) that proto.WebMessageInfo.fromObject strips because
+						// they aren't part of the proto.MessageKey schema.
+						fullMsg.key = msg.key
 						await upsertMessage(fullMsg, 'append')
 					}
 				})