feat: 전략 백테스팅 기능 추가

- Introduced a `backtest_strategy` endpoint to enable strategy backtesting with user-specified parameters.
- Implemented a generic backtesting engine allowing rebalancing, equity curve tracking, and performance metric calculations.
- Added `BacktestMixin` for strategies to support backtesting-related operations.
- Extended BAA strategy to support backtesting with ticker data download and portfolio simulation.
- Updated `urls.py` to include the new backtesting endpoint.
- Enhanced logging and error handling throughout the backtesting process.

strategies/urls.py

@@ -4,6 +4,7 @@ from . import views
 urlpatterns = [
     path('strategies/', views.list_strategies, name='list_strategies'),
     path('strategies/execute/', views.execute_strategy, name='execute_strategy'),
+    path('strategies/backtest/', views.backtest_strategy, name='backtest_strategy'),
     path('strategies/implementations/', views.list_available_implementations, name='list_available_implementations'),
     path('executions/<int:execution_id>/', views.execution_status, name='execution_status'),
 ]