[vitest-pool-worker] Add type: module in package.json

[vicb]

Building vitest-pool-worker fails for some Node version (i.e. 22.5.1, 20.18.1).

@cloudflare/vitest-pool-workers:build: file:///Users/vberchet/code/work/workers-sdk/packages/vitest-pool-workers/scripts/rtti/query.mjs:3
@cloudflare/vitest-pool-workers:build: import { StructureGroups } from "./rtti.js";
@cloudflare/vitest-pool-workers:build:          ^^^^^^^^^^^^^^^
@cloudflare/vitest-pool-workers:build: SyntaxError: Named export 'StructureGroups' not found. The requested module './rtti.js' is a CommonJS module, which may not support all module.exports as named exports.
@cloudflare/vitest-pool-workers:build: CommonJS modules can always be imported via the default export, for example using:
@cloudflare/vitest-pool-workers:build: 
@cloudflare/vitest-pool-workers:build: import pkg from './rtti.js';
@cloudflare/vitest-pool-workers:build: const { StructureGroups } = pkg;
@cloudflare/vitest-pool-workers:build: 
@cloudflare/vitest-pool-workers:build:     at ModuleJob._instantiate (node:internal/modules/esm/module_job:171:21)
@cloudflare/vitest-pool-workers:build:     at async ModuleJob.run (node:internal/modules/esm/module_job:254:5)
@cloudflare/vitest-pool-workers:build:     at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:485:26)
@cloudflare/vitest-pool-workers:build:     at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:109:5)
@cloudflare/vitest-pool-workers:build: 
@cloudflare/vitest-pool-workers:build: Node.js v22.5.1
@cloudflare/vitest-pool-workers:build:  ELIFECYCLE  Command failed with exit code 1.

Adding an explicit module type fixes the issue.

/ref #9495

/cc @jamesopstad @edmundhung

---

• Tests
  • TODO (before merge)
  • Tests included
  • Tests not necessary because: depends on the installed Node version, not caught by CI but tested locally with 22.5.1
• Wrangler / Vite E2E Tests CI Job required? (Use "e2e" label or ask maintainer to run separately)
  • I don't know
  • Required
  • Not required because:
• Public documentation
  • TODO (before merge)
  • Cloudflare docs PR(s):
  • Documentation not necessary because: bug fix
• Wrangler V3 Backport
  • TODO (before merge)
  • Wrangler PR:
  • Not necessary because: in vite-pool-worker

[changeset-bot]

🦋 Changeset detected

Latest commit: e8a2f2e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/vitest-pool-workers	Patch

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commit: e8a2f2e