fix: prevent Vitest from hanging

[eltigerchino]

fixes #13368

I thought #12830 fixed this but on testing again it doesn't. This PR builds upon it be delaying the call of getPlatformProxy even further, calling it only once when platform is accessed. The last PR was also missing a changeset for the cloudflare workers adapter.

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🦋 Changeset detected

Latest commit: 08170a9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@sveltejs/adapter-cloudflare-workers	Patch
@sveltejs/adapter-cloudflare	Patch

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