v 1.7.0 isWorkerRuntime not available on ESM

```json
{
"threads": "^1.7.0",
}
```

```shell
❯ cat node_modules/threads/worker.mjs
import WorkerContext from "./dist/worker/index.js"

export const expose = WorkerContext.expose
export const registerSerializer = WorkerContext.registerSerializer
export const Transfer = WorkerContext.Transfer
```

```typescript
import { expose, isWorkerRuntime } from 'threads/worker';
^^^^^^^^^^^^^^^
SyntaxError: The requested module 'threads/worker' does not provide an export named 'isWorkerRuntime'
at ModuleJob._instantiate (node:internal/modules/esm/module_job:123:21)
at ModuleJob.run (node:internal/modules/esm/module_job:189:5)
at async Promise.all (index 0)
at ESMLoader.import (node:internal/modules/esm/loader:530:24)
at loadESM (node:internal/process/esm_loader:91:5)
at handleMainPromise (node:internal/modules/run_main:65:12)
```