chore: add tests for treeshaking

[eltigerchino]

related to #13738

This PR adds a test to ensure that the browser and dev conditions from the $app/environment module are treeshaken. This will make the rolldown-vite ecosystem ci fail again since treeshaking isn't on par with Rollup yet rolldown/rolldown#3403

If you want to see the Rolldown output, you can add the rolldown-vite override and run the tests.

    "overrides": {
        "vite": "npm:rolldown-vite@beta"
    }

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[dominikg]

above browser was changed to client, do we have to update this check too?

[eltigerchino]

The checks are actually checking for the browser and dev imports from $app/environment rather than the string itself. Both shouldn't be in the output though if the treeshaking is done correctly. I changed it from "not browser" to "server" because that was causing this assertion to fail.

[dummdidumm]

clarified with a comment - nice work!