adjust pd.read_csv args to remove ParserWarning

[yufengg]

Add engine="python" to pd.read_csv calls

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[divyashreepathihalli]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly resolves a ParserWarning in pandas by explicitly setting engine="python" in pd.read_csv calls that use a multi-character separator. The change is consistently applied to the Python script, Jupyter notebook, and Markdown versions of the sequential_retrieval example. This is the standard way to address this warning and has no performance impact in this context, as the Python engine was already being used as a fallback. The implementation is clean, effective, and I have no suggestions for improvement.