improve support for environment api
#1137currently vite-plugin-svelte still uses the ssr flag passed to hooks, this only works due to vites fallback support.
switch to this.environment information and also see what we can do with the compile cache and possibly handleHotUpdate (ssr module invalidation)
keep as is, but it might lead to less optimal usage with environment api
would make my life easier
fixed in #1145 released in 6.0.0-next.2