🐛 Watchdog: [LOW] Fix integration test failing due to container padding on speed test

[AEmotionStudio]

This PR updates the test_speed test in test_integration.py to check the audio stream duration rather than the container duration. This is needed because the test uses very short FFMPEG clips, and container padding can obscure actual video length changes when adjusting speed.

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PR created automatically by Jules for task 178459064229417938 started by @AEmotionStudio

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