Replace yup with zod

[bradenmacdonald]

This repo uses a very old version of "yup" for data validation. Replace it with zod which is more popular, has better typescript support, and results in a smaller bundle.

They are similar and yup is only used in a dozen places, so it should not be too difficult to do.

[bashward]

Hi @bradenmacdonald! I'd love to work on this. Can this be assigned to me?

[bradenmacdonald]

@bashward Sure, done! Feel free to ping me for review / input as needed. Thanks :)