⚡ Bolt: Caching Printify Variant Fetches

[merg357]

💡 What: Memoized get_variants in printify_manager.py using @functools.lru_cache and cast its response to an immutable tuple to avoid side-effects.
🎯 Why: Prevents repeated (N+1) API calls when repeatedly requesting identical blueprint variants during the bulk product creation loop.
📊 Impact: Considerably reduces the number of network requests sent to the Printify API during bulk operations.
🔬 Measurement: Verify by executing the create loop which will complete noticeably faster.

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PR created automatically by Jules for task 8547418131812005411 started by @merg357

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