chore: convert lib/utils.js to ESM

[arun-357]

PR Checklist

• Addresses an existing open issue: fixes 🛠️ Repo: Convert lib/utils.js to ESM #5964
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Part of #5400. Renames lib/utils.js → lib/utils.mjs and converts it to ESM named exports, updating every runtime call site and test in the same change. No behavior change.

• Each exports.X = … becomes an inline export function/export const; internal exports.X self-references are now direct calls. No default/aggregate export (per AGENTS.md).
• Call sites updated to match: CJS consumers require("./utils.mjs"), ESM named-import consumers from "./utils.mjs", and namespace consumers switched from import utils from to import * as utils from (a default import of a named-export module is undefined).
• Tests: sinon cannot stub ES modules, so the sinon.stub(utils, …) calls were reworked — the unasserted isString/noop stubs were removed, and the isBrowser stubs were replaced with process.browser toggling (isBrowser() is Boolean(process.browser), so the same code path and assertions run). rewiremock keys/import paths were repointed to .mjs.

Verified: test-node suites, test-smoke, eslint, tsc, and a clean+build browser bundle all pass; lib/utils.js was not listed in package.json's browser map, so no config change was needed.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: arun-357 / name: arun-357 (cce77da)

[mark-wiemer]

Can you explain how these tests aren't false negatives with this change?

[arun-357]

nothing ever asserted on these stubs, so they weren't testing anything

[codecov]

Codecov Report

❌ Patch coverage is 17.07317% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.33%. Comparing base (fb1998a) to head (cce77da).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/utils.mjs	0.00%	34 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6071      +/-   ##
==========================================
- Coverage   78.12%   72.33%   -5.80%     
==========================================
  Files          63       63              
  Lines        4590     4587       -3     
  Branches      977      981       +4     
==========================================
- Hits         3586     3318     -268     
- Misses       1004     1269     +265     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.