fix(backtest): resolve mypy and ruff lint issues

- dsl.py: use NDArray type annotations, fix None narrowing
- cli.py: add type annotations, fix import sorting
- strategy.py: fix UP038 isinstance, add noqa for I() method name
- tests: fix E712 bool comparison assertions

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/settings.local.json

@@ -72,7 +72,11 @@
       "Bash(gh auth *)",
       "Bash(rm -rf easy_tdx.wiki)",
       "Bash(gh repo *)",
-      "Bash(gh api *)"
+      "Bash(gh api *)",
+      "Bash(mypy src/easy_tdx/backtest/types.py)",
+      "Bash(mypy tests/unit/test_backtest_types.py)",
+      "Bash(mypy src/easy_tdx/backtest/types.py tests/unit/test_backtest_types.py)",
+      "Bash(mypy *)"
     ]
   }
 }