standalone version for Extism interop?

Howdy! I know its been mentioned in passing, but I figure an issue to track would be worth creating. I am curious if we could bridge language support here with Extism, and could leverage a standalone wasm build. I see there are some Emscripten imports[0] fulfilled by JS APIs, e.g. `env::emscripten_date_now`, which would be possible to stub. Curious if you could point to any docs or build info on where to dig a little deeper?

Great work, very cool to see this :)

[0]: https://modsurfer.dylibso.com/module?hash=14a548392be7044caa124eaae973a57c194251a4bb7b7cc1e3256538ff59b41a