feat: support jspi on available platforms

[chrisdickinson]

This allows us to use async host functions on the main thread on supported platforms. (Right now that's just Node v23+, as far as I know.)

Additionally: this PR also removes WASIp1 support for Deno, since WASI support is broken there as of Deno v2.

Example use:

const functions = {
  'extism:host/user': {
    async hello_world(context: CallContext, off: bigint) {
      await new Promise(resolve => setTimeout(resolve, 100))
      return context.store('wow okay then');
    },
  },
};

const plugin = await createPlugin(
  { wasm: [{ url: 'http://localhost:8124/wasm/code-functions.wasm' }] },
  { useWasi: true, functions },
);

try {
  const output = await plugin.call('count_vowels', 'hello world');
  assert.equal(output?.string(), 'wow okay then');
} finally {
  await plugin.close();
}

(Note: there might still be a good reason to keep background-worker around since –AFAICT– suspending Wasm still blocks the main thread while executing. However, we might be able to make the threaded version a lot nicer! Now that we can await in host functions on the background thread, we don't need to atomically copy data down from the host anymore, we can just postMessage the new blocks down. Best of both worlds! This represents future work outside the scope of this PR, however.)

[zshipko]

This is awesome! As I mentioned in a comment I'm slightly out of my depth here but from what I can tell the updates look good. Windows CI is failing, but once that is fixed I am in favor of merging this.

I know you mentioned background plugins are slower in the benchmark PR, would this have the potential to improve performance while still enabling async functions?

[zshipko]

This is when I realized I knew nothing about JS. Usually it happens a little further down the diff 😅

[chrisdickinson]

I know you mentioned background plugins are slower in the benchmark PR, would this have the potential to improve performance while still enabling async functions?

Yep! On platforms that support JSPI, we should be able to instantiate foreground plugins that use async host functions, which clocked in at around 190-231 microseconds per instantiation.