⚡ Bolt: Eliminate LINQ allocations in RobotMerger.Process

[lordhippo]

💡 What: Replaced a heavy LINQ chain (SelectMany, GroupBy, ToDictionary, ToList) in RobotMerger.Process with a pre-allocated, reused Dictionary<RobotId, List<RobotTracker>> that is cleared and repopulated via explicit loops each frame.

🎯 Why: The previous LINQ chain was allocating an enumerator, multiple IGrouping objects, a new Dictionary, and a new List for every robot on the field (~16 lists), every single frame (~100Hz). This caused significant, constant GC pressure in the Vision pipeline.

📊 Impact: Eliminates ~16 List<RobotTracker> allocations, 1 Dictionary, and multiple IGrouping/enumerator allocations per frame. At 100Hz, this is a savings of over 1,800 objects allocated per second on the gen-0 heap.

🔬 Measurement: Verify with dotnet-counters monitor --counters System.Runtime[gen-0-gc-count,alloc-rate] before and after the change to observe the drop in alloc-rate.

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PR created automatically by Jules for task 8838176449451776364 started by @lordhippo

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