Replace run-parallel-limit with p-limit and use native promises

[Copilot]

Overview

Fixes #823

Replaces the run-parallel-limit dependency with p-limit in just-scripts, and converts the affected tasks to use native promises inline rather than wrapping the old callback pattern.

• cleanTask: now an async task that awaits Promise.all of limited fse.remove(path) promises (no callback wrapper).
• copyTask: collects src/dest pairs, then awaits limited copies using pipeline from stream/promises instead of the callback form of pipeline.
• sassTask: async task awaiting limited per-file work; compile() and postcss(...).process() are awaited inline. Only the legacy node-sass render() callback API is promisified, since it has no promise-based equivalent.
• Dependencies: added p-limit (^7.3.1), removed run-parallel-limit and @types/run-parallel-limit.

p-limit v7 is ESM-only, so it is dynamically imported from CJS the same way nano-spawn already is elsewhere in the package.

A Beachball change file is included.

Test Notes

• Existing tests for all three tasks pass. Two test-side adjustments were needed for the promise conversion:
  • cleanTask.spec.ts: the fs-extra.remove mock is now promise-based instead of callback-based.
  • copyTask.spec.ts: preloads the ESM-only p-limit in beforeAll, since it cannot be loaded from disk while mock-fs is active.
• Validated from the repo root: yarn build, yarn test, yarn lint, yarn format:check, yarn api:update (no API report changes).

[Copilot]

Pull request overview

This PR updates just-scripts to remove the run-parallel-limit callback-based concurrency helper, replacing it with p-limit and converting the affected tasks to promise-first async implementations (including using stream/promises for copy streaming). This aligns the task implementations with modern Node.js behavior while preserving concurrency limits and existing task semantics.

Changes:

• Replaced run-parallel-limit / @types/run-parallel-limit with p-limit (ESM-only, loaded via dynamic import) in just-scripts.
• Converted cleanTask, copyTask, and sassTask to async tasks using native promises and Promise.all + concurrency limiting.
• Updated tests to accommodate promise-based behavior and ESM-only import constraints under mock-fs.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Removes run-parallel-limit and adds p-limit (+ transitive yocto-queue) to the lockfile.
packages/just-scripts/package.json	Swaps the runtime dependency to p-limit and drops @types/run-parallel-limit.
packages/just-scripts/src/tasks/cleanTask.ts	Converts to async + p-limit-throttled fse.remove promises.
packages/just-scripts/src/tasks/copyTask.ts	Converts to async + p-limit, and switches to pipeline from stream/promises.
packages/just-scripts/src/tasks/sassTask.ts	Converts to async + p-limit; awaits compile/postcss steps inline and promisifies legacy render().
packages/just-scripts/src/tasks/tests/cleanTask.spec.ts	Updates the fs-extra.remove mock to be promise-based.
packages/just-scripts/src/tasks/tests/copyTask.spec.ts	Preloads p-limit in beforeAll to avoid ESM load issues under mock-fs.
change/change-21b37dad-e52f-40ef-937e-eb775c98f1e9.json	Adds a Beachball change file documenting the dependency/task updates.

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