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/Types/Socket.ts

@@ -229,4 +229,27 @@ export type SocketConfig = {
 	 * WARNING: Setting to 0 disables limit and allows potential memory leaks!
 	 */
 	maxSocketClientListeners?: number
+
+	// === Unified Session Telemetry ===
+
+	/**
+	 * Enable unified_session telemetry to reduce detection of unofficial clients.
+	 *
+	 * When enabled, sends time-based session identifiers that mimic official
+	 * WhatsApp Web client behavior. This may help reduce "Your account may be
+	 * at risk" warnings, though effectiveness is not guaranteed.
+	 *
+	 * Telemetry is sent at specific trigger points:
+	 * - After successful login
+	 * - After successful pairing
+	 * - When sending 'available' presence
+	 *
+	 * Can also be controlled via environment variable:
+	 * BAILEYS_UNIFIED_SESSION_ENABLED=true|false
+	 *
+	 * @default true
+	 * @see https://github.com/tulir/whatsmeow/pull/1057
+	 * @see https://github.com/WhiskeySockets/Baileys/pull/2294
+	 */
+	enableUnifiedSession?: boolean
 }