fix: serialize parallel test results without mutating user objects

[GrahamCampbell]

PR Checklist

• Addresses an existing open issue: 🐛 Bug: parallel mode serializer mutates objects reachable from a test's error in place, corrupting shared modules for the reused worker and losing the file's results #6053 (v11.x backport of fix: serialize parallel test results without mutating user objects #6056)
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Backport of #6056 to v11.x, the current stable line. The serializer here (lib/nodejs/serializer.js) is identical to main's serializer.mjs apart from the CJS/ESM module wrappers, so the change transposes one-to-one — see #6056 for the full description of the bug and the fix.

On this branch the full node-unit suite passes (598 tests, including the 20 new serializer regression tests), as do the parallel integration specs (circular-reference and getter fixtures) and an end-to-end run of the #6053 repro: the original failure is reported, and require('crypto') keeps its functions in the reused worker.

[github-actions]

👋 Hi @GrahamCampbell, thanks for the pull request! A scan flagged a concern with it. Could you please take a look?

[pr-task-completion] This PR's body is missing [x] checks on the following tasks from the PR template.

• That issue was marked as status: accepting prs

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[mark-wiemer]

Marking as draft until backing issue is out of triage