Detect Expensive Map Iteration in Soroban

# 🧠 Concept  
Detect gas-heavy iteration over Soroban maps.

## ⚠️ Problem  
Large iteration loops increase execution cost.

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

## ✅ Requirements  
- Detect iteration-heavy patterns  
- Suggest pagination/chunking  

## 🎯 Acceptance Criteria  
- [ ] Expensive map iteration detected  