Make workerUrl fetch bundler-agnostic

[stylessh]

When almostnode's library is built by Vite, new URL('./worker/runtime-worker.ts', import.meta.url) in WorkerRuntime is transformed into new Worker(new URL("/assets/runtime-worker-<hash>.js", import.meta.url), ...) in dist/index.mjs.

Turbopack (and Webpack) statically analyze new URL(..., import.meta.url) at build time and fail when the path is a server-relative /assets/... URL — they can't find the file in the consuming project's asset pipeline.

The fix in practice

Before (breaks Turbopack/Webpack — they try to resolve the asset at build time):

// consumer code
const runtime = await createRuntime(vfs, { useWorker: true, dangerouslyAllowSameOrigin: true });
//                                         ^ internally uses new URL("/assets/runtime-worker-HASH.js", import.meta.url)
//                                           Turbopack: __turbopack_context__.x is not a function

After (works with any bundler):

// app/api/almostnode-worker/route.ts
import { getWorkerContent } from 'almostnode/next';
export async function GET() {
  return new Response(getWorkerContent(), { headers: { 'Content-Type': 'application/javascript' } });
}

// In your component
const runtime = await createRuntime(vfs, {
  useWorker: true,
  dangerouslyAllowSameOrigin: true,
  workerUrl: '/api/almostnode-worker',  // ← bypasses the static analysis entirely
});

The default behavior (no workerUrl) is unchanged — Vite users are unaffected.