[TASK][Timpani-n] Notify connected nodes of shutdown

[LGSI-KarumuriHari]

📝 Task Description

Coordinate shutdown across distributed nodes via notification.

📋 Checklist

• Implement shutdown notification message
• Send notification to timpani-o orchestrator
• Notify peer timpani-n nodes if applicable
• Wait for acknowledgment with timeout
• Proceed with shutdown after notifications
• Handle notification failures gracefully

🔗 Related Requirement

Relates to #23 (Signal Handling)
Relates to #15 (Implement Signal Handling)
Relates to gRPC communication

📐 Implementation Guidelines

• Functional Requirement: FR-7.3.4 - Notify connected nodes of shutdown
• Component: timpani-n/Execution Layer/Signal Handler
• Send shutdown notification via gRPC to timpani-o
• Include node ID and shutdown reason
• Allow brief timeout for notification (e.g., 1 second)
• Proceed with shutdown even if notification fails

🧪 Testing Method

• Unit test: Verify notification message format
• Integration test: Test notification delivery
• Network failure test: Test shutdown with network down

[jayakrishnan04b]

@basheerFZ Please assign this feature implementation to me.