⚡ Bolt: Memoize static Printify variant queries to fix N+1 API bottleneck

[merg357]

💡 What: Added @functools.lru_cache to get_variants in printify_manager.py and updated it to return an immutable tuple.
🎯 Why: The script repeatedly fetched the same static blueprint variants in a nested loop for each design uploaded, causing an N+1 network bottleneck.
📊 Impact: Eliminates duplicate network requests for identical blueprints, saving hundreds of milliseconds per product creation iteration.
🔬 Measurement: Verify the execution time reduction when running python3 printify_manager.py create with multiple designs.

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PR created automatically by Jules for task 14368208072914822734 started by @merg357

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