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/WAUSync/USyncUser.ts

@@ -2,6 +2,8 @@ export class USyncUser {
 	id?: string
 	lid?: string
 	phone?: string
+	username?: string
+	usernameKey?: string
 	type?: string
 	personaId?: string
 
@@ -20,6 +22,16 @@ export class USyncUser {
 		return this
 	}
 
+	withUsername(username: string) {
+		this.username = username
+		return this
+	}
+
+	withUsernameKey(usernameKey: string) {
+		this.usernameKey = usernameKey
+		return this
+	}
+
 	withType(type: string) {
 		this.type = type
 		return this