⚡ Bolt: Cache ML models in memory to prevent repeated disk loading

[benpiper]

💡 What: Added @functools.lru_cache(maxsize=1) to globally cache large ML models in processor.py and background_remover.py.
🎯 Why: Prevents severe performance bottlenecks and potential Out-Of-Memory (OOM) issues from reloading large models from disk repeatedly during processing.
📊 Impact: Eliminates redundant model loading time, significantly improving processing speed and memory stability.
🔬 Measurement: Verify by running uv run pytest and observing faster subsequent model executions.

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PR created automatically by Jules for task 2148709266997561254 started by @benpiper

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