style(tests): ruff format 修复尾随空行（CI ruff format --check 失败）

tests/unit/test_backtest_portfolio.py

@@ -358,4 +358,3 @@ def test_apply_trades_timestamp_vs_int_df() -> None:
 
     # 修复前交易被丢弃、持仓为 0
     assert tracker.positions["size"].iloc[0] == 100
-

tests/unit/test_portfolio_rebalance.py

@@ -129,4 +129,3 @@ class TestRebalanceEngine:
         result = engine.run(_make_market(), start_date=20240101, end_date=20240430)
         md = result.performance["max_drawdown"]
         assert 0.0 <= md <= 1.0, f"max_drawdown={md} 应落在 [0,1]"
-