chore(mimalloc-safe): update to a bug-fix branch for verification

[shulaoda]

See napi-rs/mimalloc-safe#71 & https://github.com/rolldown/rolldown/actions/runs/26264825278/job/77305893292

This is temporarily merged to allow upgrade and integration, and will be validated in subsequent CI runs. It has already been confirmed to work in the current PR. It will be reverted before the next release, and mimalloc-safe will switch back to the official release version for production use.

[netlify]

✅ Deploy Preview for rolldown-rs canceled.

Name	Link
🔨 Latest commit	ac87964
🔍 Latest deploy log	https://app.netlify.com/projects/rolldown-rs/deploys/6a0fc5f79d94640008c0ac88

[codspeed-hq]

Merging this PR will not alter performance

✅ 4 untouched benchmarks
⏩ 10 skipped benchmarks¹

---

_{Comparing 05-22-chore_mimalloc-safe_update_to_a_bug_fixed_branch_to_verify_it (ac87964) with main (e412df1)}

Footnotes

1. 10 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩