⚡ Bolt: Cache large ML models to prevent repeated disk loading

[benpiper]

💡 What: Cached OpenAI Whisper and RVM models globally using functools.lru_cache(maxsize=1).
🎯 Why: Loading large ML models from disk on every invocation was a severe performance bottleneck and risked OOM errors.
📊 Impact: Eliminates repeated disk I/O, reducing model initialization time to near zero for subsequent jobs.
🔬 Measurement: Verify by running consecutive video processing jobs and observing the reduced time spent in model loading.

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PR created automatically by Jules for task 17137370608047713031 started by @benpiper

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