package infrastructure updates

[topepo]

• air was used to format code
• R dependency is not >= 4.1.0
• Transition to base R pipe
• Transition errors and warnings to use the cli package
• update GHA
• Move (mostly) away from using .data$ prefixes in dplyr selections
• Declare a many-to-many join
• Reorganize tests a bit; use a helper file, 3rd edition of testthat, etc
• Declare some variables used in tidyselect to avoid global variable check false positives

[topepo]

A little more to do. I made a draft PR just to see if the new GHAs work well.

[topepo]

Initial changes for #28

@holub008 it is ready for review!

[holub008]

Thanks for the modernization and love the formatting consistency

[topepo]

I think it's ready to merge. Thanks!

[holub008]

Thanks Max, you're great!