Only the content of nix_dev_env.md changed significantly. The content of the nix_*_{setup,workflows}.md are copy and pasted from the the existing dev_environment.md with exception of initial headers.

Hey @jon, can you split this diff into two, per this Notion doc? I made a similar diff once (D4399) which was quite confusing because I moved stuff and edited stuff in the same diff. You can update this one to just copy and pasting stuff from dev_environment.md and then stack another one on top of this to update nix_dev_env.md. The factoring makes it easier to review.

Moving code around: D4399
Updating code: D4414

It would also make it easier to accept the first one since it's just copied from dev_environment.md. Thanks.