Replace `dotenv` with builtins

[aklinker1]

Feature Request

See Vite's loadEnv imlementation - they use dotenv-expand and node:util#parseEnv.

https://github.com/vitejs/vite/blob/a704abc4e6f1528837030cf92cb7a2de65da54cc/packages/vite/src/node/env.ts

[HarrysonLadines]

Hi, I'd like to work on this. Can you assign it to me?