fix: Stub out __VITE_PRELOAD__ during prerender

[rschristian]

Closes #125

Dynamic imports now result in something like this:

(()=>import("./index-kayMhHeV.js"),__VITE_PRELOAD__)

Which then throws as Vite hasn't subbed it out.

It used to be a string like so:

(()=>import("./index-kayMhHeV.js"),"__VITE_PRELOAD__")

for reasons even the Vite team wasn't clear on (see reference in change)