feat(nuxt): Don't run source maps related code on Nuxt "prepare"

[github-actions]

Note

The pull request "feat(nuxt): Don't run source maps related code on Nuxt "prepare"" was created by @s1gr1d but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

Stumbled upon this while working on something else. The source map related code was always executed on the package manager's install command and as nuxi prepare runs on postinstall. This step is only important for generating the types, so we can skip all source map related things here so this only runs during the actual build.

I also changed the console log a bit so it's more clear what we are doing.

Nuxt docs: https://nuxt.com/docs/4.x/api/commands/prepare

[linear]

JS-1532