feat(audio): add tracking for audio transcriptions in OpenAI client

[JasonLovesDoggo]

This adds support for tracking transcriptions from OpenAI. It does this via a new event $ai_transcription which follows the pattern of embeddings. I figure that audio -> text Is different enough from text-to-text to deserve its own event.

Confirmed it worked in my own testing. Feel free to impersonate and view https://us.posthog.com/project/254263/events/2e8ded5c-acd2-45b4-b10f-7a85a438ffaa/2026-01-02T15%3A02%3A00.007000-05%3A00

[greptile-apps]

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[Copilot]

Pull request overview

This PR adds tracking support for OpenAI audio transcriptions via a new $ai_transcription event. The implementation follows the existing pattern used for embeddings, treating audio-to-text as a distinct operation from text-to-text transformations.

• Introduces WrappedAudio and WrappedTranscriptions classes for both sync and async OpenAI clients
• Captures transcription metadata including model, input file name, output text, latency, and optional properties like language and audio duration
• Supports privacy mode, groups, and custom properties consistent with other AI tracking features

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
posthog/ai/openai/openai.py	Adds WrappedAudio and WrappedTranscriptions classes to track transcription usage in the sync OpenAI client
posthog/ai/openai/openai_async.py	Adds async versions of WrappedAudio and WrappedTranscriptions to track transcription usage in the async OpenAI client
posthog/test/ai/openai/test_openai.py	Adds comprehensive test coverage for transcription tracking including basic usage, duration tracking, language parameter, groups, privacy mode, and async support

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[JasonLovesDoggo]

cc @andrewm4894