chore: make benchmark to read subfolders and three groupby benchmarks.

[Genesis929]

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Fixes #<issue_number_goes_here> 🦕

[milkshakeiii]

---BIGQUERY USAGE REPORT---
visualization/bq_dataframes_covid_line_graphs.ipynb - query count: 2, bytes processed sum: 12948886977, slot millis sum: 31010420
generative_ai/bq_dataframes_llm_kmeans.ipynb - query count: 20, bytes processed sum: 4137546100, slot millis sum: 2097125
dataframes/dataframe.ipynb - query count: 44, bytes processed sum: 5598362, slot millis sum: 170966
regression/easy_linear_regression.ipynb - query count: 16, bytes processed sum: 151961, slot millis sum: 139131
getting_started/getting_started_bq_dataframes.ipynb - query count: 19, bytes processed sum: 204521, slot millis sum: 124841
dataframes/index_col_null.ipynb - query count: 16, bytes processed sum: 4596839, slot millis sum: 35759
dataframes/integrations.ipynb - query count: 7, bytes processed sum: 270, slot millis sum: 26118
generative_ai/large_language_models.ipynb - query count: 4, bytes processed sum: 7260, slot millis sum: 10742
location/regionalized.ipynb - query count: 162, bytes processed sum: 1595325, slot millis sum: 678236
remote_functions/remote_function.ipynb - query count: 12, bytes processed sum: 86086638598, slot millis sum: 12955024
regression/sklearn_linear_regression.ipynb - query count: 17, bytes processed sum: 135165, slot millis sum: 289204
---total queries: 319, total bytes: 103185361378, total slot millis: 47537566---

LGTM!