fix(kernel): use as_chunks for POSIX ACL parsing

[NathanFlurry]

• Replace deprecated chunks_exact ACL parsing with stable as_chunks.
• Preserve the existing POSIX ACL validation behavior.

[the-company-company]

Co · session: Fix agentos main CI (clippy 1.98 + browserbase types)

• Auto-fix ; feedback on this pull request flows to the session and gets addressed
• Review ; Co reviews new pushes

_{@co <ask> hands Co a task · @co mute pauses · @co archive ends the session}

[railway-app]

🚅 Environment agentos-pr-1969 in rivet-frontend has no services deployed.

[the-company-company]

✅ No issues found

_{Reviewed commit 6c39ca3.}