breaking: make getRequest and setResponse synchronous

[Rich-Harris]

Not sure why these were ever async. They don't need to be. The danger of course is that one day they might need to be, but I'm not sure why that would be the case.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 1f6724a:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/1f6724af850566c96abbc0b059221768887f0af2

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16280

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16280-svelte.vercel.app/