fix: scripts maintenance

[mrain]

closes: #614

This PR:

• Fix the test code coverage script.
• Add the unstable option back for run_test.sh . Now it also report the test running time.

This PR does not:

Key places to review:

---

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• [ ] Targeted PR against correct branch (main)
• [ ] Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• [ ] Wrote unit tests
• [ ] Updated relevant documentation in the code
• [ ] Added relevant changelog entries to the CHANGELOG.md of touched crates.
• [ ] Re-reviewed Files changed in the GitHub PR explorer

[mrain]

it's great that cargo +nightly works under nix now. previously I remember that even if we have the nightly toolchain (for fmt at least), this command won't work.

but i just tested now, it works.

I remember that it was the problem with displaydoc. Rust was tuning some feature that will cause compilation error. Now there're only warnings not errors.