pub fn get_preloaded(&self, url: &PathMaybeWithLocale) -> Option<PageDataPartial> {
        let mut preloaded = self.preloaded.borrow_mut();
        let mut route_preloaded = self.route_preloaded.borrow_mut();
        if let Some(page_data) = preloaded.remove(url) {
            Some(page_data)
        } else {
            route_preloaded.remove(url)
        }
    }
Gets a preloaded page. This will search both the globally and
route-specifically preloaded pages.

Note that this will delete the preloaded page from the preload cache,
since it's expected to be parsed and rendered immediately. It should
also have its head entered in the PSS.
packages/perseus/src/state/state_store.rs