devtools don't work with Bun: Avoid using NODE_ENV in devtools server code

[obadakhalili]

when running the devtools bin with bun using bunx --bun devtools in user's codebase, the lib doesn't work properly and runs in dev mode for the user if they have a .env file with the value NODE_ENV set to development because bun auto loads the user's vars from the .env file. I don't think its wise to use environment variables in libraries' code because users' environments can affect the runtime behaviour, especially so for popular runtime variables such as NODE_ENV.

I also noticed that the devToolsMiddleware function also uses NODE_ENV to throw an error if the user using this in production. i think the same reasoning against env vars in libraries' code applies again, but its less harmful here.

I checked that this fix works but pointing to the local build for the devtools code from my own project where i encountered the code and made sure that bunx --bun devtools works (not in dev mode) even if i have a .env file with NODE_ENV set to development.

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)