feat: medium priority improvements

- Add 30 edge case tests (zero volume, empty data, extreme values,
  strategy reset, notifier failures)
- Fix VWAP division by zero on zero-price candles
- Add DB transaction rollback on errors + transaction() context manager
- Add parameter validation to all 7 strategies with 41 validation tests
- Fix lint issues across test files

1 files changed, 6 insertions, 4 deletions

diff --git a/tests/edge_cases/test_empty_data.py b/tests/edge_cases/test_empty_data.py
index 2449b90..ebd8467 100644
--- a/tests/edge_cases/test_empty_data.py
+++ b/tests/edge_cases/test_empty_data.py
@@ -1,18 +1,20 @@
 """Tests for empty/zero data edge cases."""
 
 import sys
-from datetime import datetime, timezone, timedelta
+from datetime import timedelta
 from decimal import Decimal
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "services" / "strategy-engine"))
 sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "services" / "backtester" / "src"))
 sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "services" / "order-executor" / "src"))
-sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "services" / "portfolio-manager" / "src"))
+sys.path.insert(
+    0, str(Path(__file__).resolve().parents[2] / "services" / "portfolio-manager" / "src")
+)
 
-from shared.models import Candle, Signal, OrderSide, Position
+from shared.models import Signal, OrderSide
 from backtester.engine import BacktestEngine
-from backtester.metrics import TradeRecord, compute_detailed_metrics
+from backtester.metrics import compute_detailed_metrics
 from portfolio_manager.portfolio import PortfolioTracker
 from order_executor.risk_manager import RiskManager
 from strategies.rsi_strategy import RsiStrategy