policy: Implement "Max Slippage" Guard for Uniswap Trades

[akarlaraytu]

📝 Context

DeFi agents often execute trades in low-liquidity pools. We need a safety policy to prevent the agent from getting "sandwiched" or losing money due to high slippage.

🎯 The Goal

Write a CSL policy that acts as a hard constraint for a trading bot.

Variables you can use:

• price_impact (Float): The percentage impact on the pool (e.g., 2.5 for 2.5%).
• slippage_tolerance (Float): The user's setting (e.g., 0.5).
• is_verified_pool (Boolean): Whether the token contract is verified.

Requirements:

1. BLOCK if price_impact is greater than slippage_tolerance.
2. BLOCK if price_impact > 5.0 (Hard cap, even if user allows it).
3. BLOCK if is_verified_pool is False.

📚 Resources

• Start here: docs/getting-started.md
• Check syntax: quickstart/01_hello_world.csl
• See how we handle numbers: docs/syntax-spec.md
• Reference: examples/chimera_banking_case_study.csl

✅ Definition of Done

Submit a PR with: examples/community/defi_slippage_guard.csl