feat(telemetry): add unified_session telemetry to reduce detection

Implements WhatsApp's unified_session telemetry feature to reduce
detection of unofficial clients. This is an enterprise-grade implementation
inspired by whatsmeow PR #1057 and Baileys PR #2294.

Features:
- UnifiedSessionManager class with circuit breaker protection
- Server time synchronization for accurate session IDs
- Rate limiting to prevent spam (1 minute between sends)
- Prometheus metrics integration (unified_session_sent, errors)
- Structured logging for debugging
- Configurable via SocketConfig.enableUnifiedSession
- Environment variable support (BAILEYS_UNIFIED_SESSION_ENABLED)

Trigger points (matching official WhatsApp Web):
- After successful login (CB:success)
- After successful pairing (CB:iq,,pair-success)
- When sending 'available' presence

Implementation details:
- Session ID algorithm: (now + serverOffset + 3days) % 7days
- Time constants exported from Defaults/index.ts
- Full test coverage (31 tests)

References:
- https://github.com/tulir/whatsmeow/pull/1057
- https://github.com/WhiskeySockets/Baileys/pull/2294
- https://github.com/tulir/whatsmeow/issues/810

src/Socket/chats.ts

@@ -68,7 +68,7 @@ export const makeChatsSocket = (config: SocketConfig) => {
 		getMessage
 	} = config
 	const sock = makeSocket(config)
-	const { ev, ws, authState, generateMessageTag, sendNode, query, signalRepository, onUnexpectedError } = sock
+	const { ev, ws, authState, generateMessageTag, sendNode, query, signalRepository, onUnexpectedError, sendUnifiedSession } = sock
 
 	let privacySettings: { [_: string]: string } | undefined
 
@@ -674,6 +674,14 @@ export const makeChatsSocket = (config: SocketConfig) => {
 					type
 				}
 			})
+
+			// Send unified_session telemetry when going online
+			// This mimics official WhatsApp Web client behavior
+			if (type === 'available') {
+				sendUnifiedSession('presence').catch(err => {
+					logger.debug({ err }, 'Failed to send unified_session on presence available')
+				})
+			}
 		} else {
 			const { server } = jidDecode(toJid)!
 			const isLid = server === 'lid'