[ENH] Twelve Labs async embedding support for long audio/video

[tazarov]

Summary

Add async embedding support for the Twelve Labs provider to handle audio/video content up to 4 hours.

Context

Phase 16 implements the Twelve Labs embedding function using the sync endpoint (POST /v1.3/embed-v2), which handles text, image, and audio/video under 10 minutes. The async endpoint (POST /v1.3/embed-v2/tasks) supports audio/video up to 4 hours but requires task creation and polling for completion.

Requirements

• Add async task creation via POST /v1.3/embed-v2/tasks
• Implement polling loop to check task status and retrieve results
• Support audio/video content up to 4 hours
• Integrate with the existing ContentEmbeddingFunction interface (or extend if needed)

References

• Twelve Labs Embed API v2 docs
• Audio embeddings guide