Add SafeGuard — One-line token safety library

**SafeGuard** — Solidity library for token safety checks. 2 lines to protect a DEX from scam tokens.

```solidity
using SafeGuard for address;
tokenOut.requireSafe();
```

27 scam patterns, 6 EVM chains, 0 gas for users. ERC-7913 standard.

**GitHub**: https://github.com/CryptoGenesisSecurity/safeguard
**Category**: Security / Libraries