chore: Implement remote functions using hydratable and cache

[elliott-with-the-longest-name-on-github]

This is the WIP counterpart to sveltejs/svelte#16960

Basically, we want to know that we're covering all of the use cases of remote functions before we publish the svelte core featureset so that other frameworks can build equally-impressive features.

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Latest commit: 9e1a582

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-14872-svelte.vercel.app/

[Rich-Harris]

TODO