⚡ Bolt: [performance improvement] Memoize Printify variant API queries

[merg357]

💡 What: Memoized third-party API variant queries in printify_manager.py, create_merch.py, and merch_factory.py using @functools.lru_cache(maxsize=None). The return types were explicitly converted to immutable tuple structures to prevent downstream mutations.
🎯 Why: To prevent repeating identical network requests for static configuration data (like Printify blueprint variants) within iteration loops, eliminating a severe N+1 network bottleneck.
📊 Impact: Eliminates redundant HTTP calls, significantly speeding up the iterative execution of the application's create and run loops.
🔬 Measurement: Observe faster execution and lower network overhead of the CLI run and create commands.

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PR created automatically by Jules for task 16983786550211514973 started by @merg357

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