Fix LLLeap teardown ordering in macOS integration-test exits

[Copilot]

Description

The macOS build (macos-15-xlarge, Release) job was failing in INTEGRATION_TEST_llleap because LLProcess could publish child-exit state before all ready pipe callbacks had been delivered. That let LLLeap tear itself down while final stdout/stderr data was still pending.

• Root cause

  • LLProcess::handleExit() drained at most 10 ready I/O handlers after process exit.
  • Large or bursty LLLeap traffic can leave more than 10 completions queued, especially near process shutdown.
  • LLLeap consumes child pipe events from those callbacks, so early exit notification could race ahead of final message delivery.

• Change

  • Replace the fixed 10-iteration drain with a full poll_one() loop that runs until no ready handlers remain.
  • Keep exit notification ordering unchanged otherwise: drain ready pipe work first, then publish process status.

• Effect

  • Ensures LLLeap sees all already-ready stdout/stderr callbacks before reacting to child termination.
  • Removes the shutdown race that caused the macOS llleap integration test failure.

while (mIOContext.poll_one() > 0)
{
    // Keep polling until no more handlers are immediately ready.
}

Related Issues

• Please link to a relevant GitHub issue for additional context.
  • Bug Fix: Link to an issue that includes reproduction steps and testing guidance.
  • Feature/Enhancement: Link to an issue with a write-up, rationale, and requirements.

Issue Link: relates to GitHub Actions run 29146919898 / job 86532647071

---

Checklist

Please ensure the following before requesting review:

• I have provided a clear title and detailed description for this pull request.
• If useful, I have included media such as screenshots and video to show off my changes.
• The PR is linked to a relevant issue with sufficient context.
• I have tested the changes locally and verified they work as intended.
• All new and existing tests pass.
• Code follows the project's style guidelines.
• Documentation has been updated if needed.
• Any dependent changes have been merged and published in downstream modules
• I have reviewed the contributing guidelines.

---

Additional Notes

The change is intentionally narrow: it only adjusts post-exit pipe draining in LLProcess and does not alter process-status semantics outside that ordering fix.

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}