⚡ Bolt: Cache blueprint variants to eliminate N+1 API calls

[merg357]

💡 What: Memoized get_variants using @functools.lru_cache(maxsize=None) and casted responses to immutable tuples.
🎯 Why: Prevent redundant API calls to Printify when fetching blueprint variants in loop during bulk product creation.
📊 Impact: Eliminates N+1 network request bottlenecks, significantly speeding up bulk uploads and reducing rate limit risks.
🔬 Measurement: Bulk creation logic execution time scales linearly with image processing instead of blueprint API delays.

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PR created automatically by Jules for task 14109805665917410120 started by @merg357

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