Implement Soroban Best Practices Rule Pack

# 🧠 Concept
Provide a dedicated rule pack for Soroban best practices.

## ⚠️ Problem
Projects need guidance beyond vulnerability detection.

## 📁 Implementation Scope
- `src/rules/best-practices/stellar/`

## ✅ Requirements
- Create best-practice rules
- Categorize findings
- Support rule configuration

## 🎯 Acceptance Criteria
- [ ] Rule pack implemented
- [ ] Findings generated successfully