theres a plugin called hardtime.nvim that does almost exactly what you have described. It goes a bit further and actually prevents you from doing certain things if you meet a threshold (like spamming j to go down a bunch if lines instea d of something like 15j to move 15 lines down)

https://github.com/m4xshen/hardtime.nvim

I actually recently decided to make a CLI blackjack game as well! It was a fun exercise, although my focus was more on the visuals since I enjoy making ascii graphics.

https://github.com/Chewt/cardterm