⚡ Bolt: Memoize blueprint variant API queries to resolve N+1 bottleneck

[merg357]

💡 What: Added @functools.lru_cache(maxsize=None) to get_blueprint_variants() in merg_bridge.py and changed its return type to an immutable tuple.
🎯 Why: Fixes an N+1 network bottleneck where the same blueprint provider's variants were repeatedly fetched from the Printify API during iterative bulk product creation loops.
📊 Impact: Eliminates redundant network requests, significantly reducing API latency and preventing potential rate limit errors when creating multiple products from the same blueprint.
🔬 Measurement: Time the execution of bulk product creation before and after the change; monitor API request logs to confirm the variant endpoint is only hit once per blueprint provider.

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PR created automatically by Jules for task 9598767539003711653 started by @merg357

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