⚡ Change Operation<T> to readonly record struct

[johnstrand]

💡 What: Changed Operation from a class record to a readonly record struct.
🎯 Why: Bypasses heap allocations when queuing pending collection operations into ConcurrentQueue.
📊 Measured Improvement: Reduced allocated memory per benchmark operation from 24 B to 0 B (100% allocation reduction for operation objects).

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PR created automatically by Jules for task 8671509646532158004 started by @johnstrand

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