test: run cli test cases parallel

[LingyuCoder]

Summary

This pull request includes several changes to the package.json scripts and test cases in the rspack-cli package to improve parallel execution and output path handling.

Improvements to package.json scripts:

• Updated the build:js script to run in parallel for better performance.
• Updated the test:unit script to run tests in parallel.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #9502 will not alter performance

_{Comparing ci/parallel-unit-tests (88197d0) with main (6951bea)}

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Summary

✅ 7 untouched benchmarks