Implement Soroban Contract State Snapshot Tool

# 🧠 Concept  
Capture and export Soroban contract state snapshots.

## ⚠️ Problem  
Developers need reproducible audit/debugging snapshots.

## 📁 Implementation Scope  
- `src/state/snapshots/stellar/`

## ✅ Requirements  
- Export contract state  
- Support snapshot restoration  

## 🎯 Acceptance Criteria  
- [ ] Snapshot tool implemented  