feat: use live Aave rates in backtests

[MiaMakesItHappen]

Summary

• fix Aave borrow-rate collection by matching lendBorrow rows by pool id
• inject latest saved Aave rates into backtests automatically
• add a BTC daily dataset builder and checked-in sample dataset for reproducible runs

Testing

• .venv/bin/python3 scripts/get_latest_rates.py
• PYTHONPATH=. .venv/bin/python3 worker/run_backtest.py --strategy examples/strategies/crypto_yield_arb.py --dataset examples/datasets/btc_daily --dataset-version v1

Result

Backtests now use real saved Aave supply/borrow rates instead of hardcoded assumptions.