Detect Missing TTL Extension Logic

# 🧠 Concept  
Detect contracts not extending Soroban storage TTL.

## ⚠️ Problem  
Missing TTL extension may cause state expiration.

## 📁 Implementation Scope  
- `rules/stellar/storage/ttl/`

## ✅ Requirements  
- Detect missing TTL refresh logic  
- Warn developers  

## 🎯 Acceptance Criteria  
- [ ] Missing TTL extension detected  