ci: execute workflow_by_code.ipynb in GitHub Actions (closes #1278)

[anupddas]

Summary

Closes #1278

Adds a dedicated GitHub Actions workflow that executes examples/workflow_by_code.ipynb
end-to-end on every push/PR that touches the notebook or core qlib code.

Changes

• .github/workflows/test_notebook.yml — new workflow using pytest-nbmake
• Makefile — new nbmake target (mirrors CI, runnable locally via make nbmake)
• examples/workflow_by_code.ipynb — add CI environment detection cell
• tests/test_workflow_notebook.py — fast structural tests for the notebook
• .pre-commit-config.yaml — add nbstripout hook to keep outputs stripped

How to test locally

make dev
pip install "nbmake>=1.3.5" ipykernel numba
python scripts/get_data.py qlib_data --name qlib_data_simple \
    --target_dir ~/.qlib/qlib_data/cn_data --interval 1d --region cn
make nbmake

Checklist

• CI passes on this PR
• Follows existing test_qlib_from_source.yml patterns
• Signed-off-by included (DCO)

[anupddas]

@microsoft-github-policy-service agree

[CHGY003]

感谢帮忙修改bug

[anupddas]

感谢帮忙修改bug

You're welcome! Glad I could help fix the issue. Let me know if any changes are needed once the workflows finish running.