Review fixes applied:
- format_signals_for_role accepts both list and JSON string
- Test imports aligned with actual function names
- Test assertions use actual StrategySignal keys
- Tax optimization: informative message when lot data unavailable
- Pairs trading: single batch yf.download replaces 10 sequential calls
Based on: Kakushadze & Serur, '151 Trading Strategies',
Palgrave Macmillan 2018. SSRN 3247865, DOI 10.1007/978-3-030-02792-6
Clayton Brown