code reuse

[jukent]

Pulling adjust_pop_grids into it's own module.

[github-actions]

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[jukent]

NOAA site seems to be down for scheduled maintenance today, hence link failing

[rmshkv]

Thanks for this adjustment, Julia! This looks a lot cleaner than I originally had it.

[jukent]

Great. Thanks again for all your hard work @rmshkv !

[erogluorhan]

Thanks a lot for the great content, @rmshkv , and thorough review and cleaning touchups, @jukent ! Apart from its content, this is also going to be a nice example of how to implement code for cookbook in one place and reuse and display them nicely in several chapters.