Convert codebase to ESM, mostly

[bcomnes]

This converts the codebase to esm, mainly in preparation for fixing the typedocs. Some of the parallel tests were written around sync behavior of cjs, so I preserved the sync nature of some of the test tasks.

[bcomnes]

Curious what kind of perf hit we'll take with this.

[Copilot]

Pull Request Overview

This PR converts the codebase from CommonJS to ES modules, updates test-task script extensions to .cjs, and adjusts internal imports/exports accordingly.

• Switched package.json to "type": "module" and updated npm script references to .cjs
• Rewrote lib/* and scripts/make-slink.js from require/module.exports to import/export
• Updated test-workspace task files to use .cjs extensions and adjusted require paths

Reviewed Changes

Copilot reviewed 58 out of 58 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test-workspace/tasks/config1.cjs	Point to util.cjs instead of CJS module
test-workspace/tasks/append1.cjs	Updated require path to .cjs
test-workspace/tasks/append2.cjs	Updated require path to .cjs
test-workspace/package.json	Changed all task scripts to use .cjs file extensions
scripts/make-slink.js	Converted to ESM, added fileURLToPath and __dirname shim
package.json	Switched to ESM ("type":"module") and extended test timeout
lib/spawn.js	Replaced CJS branch export with import and export default
lib/spawn-win32.js	Switched to ESM import and export default spawn
lib/spawn-posix.js	Switched to ESM import and export default spawn
lib/run-tasks.js	Converted to ESM and fixed spelling of “fulfilled”
lib/run-task.js	Converted to ESM imports/exports and updated ansi-styles import
lib/read-package-json.js	Converted to ESM import and export default
lib/npm-run-all-error.js	Replaced module.exports with export default class
lib/match-tasks.js	Converted to ESM import and export default
lib/index.js	Converted to ESM imports/exports and fixed “sequential” spelling
lib/create-prefix-transform-stream.js	Converted to ESM import and export default
lib/create-header.js	Converted to ESM and replaced module.exports
eslint.config.js	Converted to ESM config and simplified neostandard import
.knip.jsonc	Updated entry glob to match .cjs task files

Comments suppressed due to low confidence (2)

lib/run-task.js:15

• [nitpick] Since you're statically importing ansi-styles, the variable ansiStylesPromise is misleading—it’s not a promise. Consider renaming it (e.g., ansiStylesModule) and updating its usage accordingly.

import ansiStylesPromise from 'ansi-styles'

lib/run-task.js:146

• [nitpick] Awaiting a non-promise value is unnecessary here. You can directly use the imported ansiStyles object without await for clearer intent.

const ansiStyles = await ansiStylesPromise

[bcomnes]

Curious what kind of perf hit we'll take with this.

Looks to be the same, which makes sense because the tests were already bottlenecked on a much slower io operation.