chore: fix JavaScript lint errors (issue #8140)

[youzi-forge]

Relates to #8140.

Description

This pull request:

• Fixes the ESLint/import-resolver ENOENT caused by @example blocks referencing non-existent files ('./beep.js', './boop.js') in @stdlib/utils/async/map-values.

• Updates the @example blocks in:

  • lib/node_modules/@stdlib/utils/async/map-values/lib/index.js
  • lib/node_modules/@stdlib/utils/async/map-values/lib/main.js
  • lib/node_modules/@stdlib/utils/async/map-values/lib/factory.js

• Replaces placeholders with real, existing files and adds a cross-platform path join:

  var join = require('path').join;
  var files = [
    join( __dirname, '..', 'README.md' ),
    join( __dirname, '..', 'package.json' )
  ];

• No runtime logic, public API, build tooling, or Make/workflow changes. This is an example-only adjustment to prevent the linter/import resolver from attempting to stat missing paths.

Related Issues

This pull request:

• relates to Fix JavaScript lint errors #8140

Questions

No.

Other

Scope & Intent

• This PR intentionally fixes the issue only for @stdlib/utils/async/map-values (the three files listed above).
• The CI failure in Fix JavaScript lint errors #8140 is triggered by random file sampling; similar placeholder paths may exist in other utils/async/* packages.
• Therefore this PR uses Relates to (not Resolves) until the same pattern is addressed in other packages.

Why this approach (and not tooling changes)

• Keep the fix minimal and source-focused: do not modify Makefiles, workflows, or eslint recipes.
• Point examples at guaranteed-to-exist files within the package (README.md, package.json) to avoid import-resolver file-system lookups failing on non-existent placeholders.

Local Verification

• Ran locally:

  make install-node-modules && make init
  make lint-javascript-files FILES="lib/node_modules/@stdlib/utils/async/map-values/lib/{index.js,main.js,factory.js}"
  # Optional: invoke the workflow helper script on a single file
  node .github/workflows/scripts/lint_javascript_files_error_log lib/node_modules/@stdlib/utils/async/map-values/lib/factory.js

• ✅ No ENOENT occurred and no new lint errors/warnings were introduced.

Follow-up Plan

• If this approach is accepted, I will submit small, per-package PRs applying the same example-path fix to other utils/async/* modules that still reference non-existent example files. Optionally open a tracking issue to audit and replace placeholder paths across affected packages.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines

---

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Coverage Report

Package	Statements	Branches	Functions	Lines
utils/async/map-values	$\color{green}561/561$ $\color{green}+100.00\%$	$\color{green}63/63$ $\color{green}+100.00\%$	$\color{green}9/9$ $\color{green}+100.00\%$	$\color{green}561/561$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.