fix(lint): export BacktestIndexRow from domain.__all__

CI flake8 flags the import as unused without the corresponding entry
in __all__. Phase 1 missed adding it.

Author: MDUYN

investing_algorithm_framework/domain/__init__.py

@@ -109,6 +109,7 @@
     "parse_decimal_to_string",
     "parse_string_to_decimal",
     "BacktestRun",
+    "BacktestIndexRow",
     "DATETIME_FORMAT_BACKTESTING",
     "BACKTESTING_FLAG",
     "PortfolioSnapshot",