[pandas] Review recent pandas release notes

[mmcky]

It is a good idea to iterate on our pandas lectures by reviewing the recent release notes for pandas>=2.0.

https://pandas.pydata.org/docs/whatsnew/index.html

• update lecture and/or syntax
• highlight any new features that may be useful to readers
• review lectures that contain pandas code to see if we should make any updates.

[longye-tian]

Hi Matt @mmcky

There are nine lectures involving pandas, as follows; I will keep reviewing and posting updates following this comment.

• long_run_growth.md (Valid under new release, one issue related to plt.savefig. Please check the details in [long_run_growth] Review Pandas code, plt.savefig #467 )
• business_cycle.md
• inflation_history.md
• inequality.md
• prob_dist.md
• heavy_tails.md
• networks.md
• simple_linear_regression.md (reviewed by @mmcky )
• mle.md

Best,
Longye

[mmcky]

thanks @longye-tian this is great investigative work.