feat(openai): implement close() cleanup for STT

[KrishnaShuk]

Description

This PR adds robust resource cleanup to the OpenAI STT and TTS plugins. It follows the AbortController pattern established in PR #849 to ensure that any in-flight network requests to the OpenAI API are properly cancelled when an agent session is terminated.

This prevents hanging processes and improves the overall stability of the framework.

Changes Made

• plugins/openai/src/stt.ts:
  • Added a private AbortController to the STT class.
  • Implemented the close() method to trigger the abort controller.
  • Passed the abortController.signal to the OpenAI client's transcriptions.create API call, making it cancellable.

Pre-Review Checklist

• Build passes: All builds (lint, typecheck, tests) pass locally
• AI-generated code reviewed: Removed unnecessary comments and ensured code quality
• Changes explained: All changes are properly documented and justified above
• Scope appropriate: All changes relate to the PR title, or explanations provided for why they're included
• Video demo: A small video demo showing changes works as expected and did not break any existing functionality using Agent Playground (if applicable)

Testing

• Automated tests added/updated (if applicable)
• All tests pass
• Make sure both restaurant_agent.ts and realtime_agent.ts work properly (for major changes)

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Note to reviewers: Please ensure the pre-review checklist is completed before starting your review.

[changeset-bot]

🦋 Changeset detected

Latest commit: d12378a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@livekit/agents-plugin-openai	Patch

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[toubatbrian]

Looks good! Can you add a changeset?

[KrishnaShuk]

Thanks! for the review @toubatbrian. I've just added the changeset.

On that note, I've noticed that other plugins (like ElevenLabs, Google, and Cartesia) are also missing this robust close() cleanup logic.
To continue improving the framework's stability, I'd be happy to create a central tracking issue to list them all and then submit a series of small, focused PRs to implement this same AbortController pattern for each one.

Lmk if that sounds like a good plan.