⚡ Fix memory leak in ShapeArray.Remove

[google-labs-jules]

• 💡 What: Added logic to nil out the underlying array element when removing an element from ShapeArray (and effectively Struct).
• 🎯 Why: Previously, ShapeArray.Remove would swap the element to remove with the tail element (or shift the window), but left the reference to the "removed" object in the underlying array's tail. This prevented the object from being garbage collected until the array itself was reallocated or collected.
• 📊 Measured Improvement:
  • Benchmarks: Ran BenchmarkSpacePartitionAddDelete (which involves heavy add/remove).
    • Baseline: ~7.86s / op, 179.5 MB/op
    • Optimized: ~7.90s / op, 179.5 MB/op
    • Result: No significant CPU or total allocation regression. The memory leak fix primarily benefits long-lived applications where Struct persists and shapes are removed, preventing gradual heap growth. The short-lived benchmark doesn't capture this long-term retention.
  • Verification: Added TestShapeArray_Remove_MemoryLeak which explicitly checks that the underlying array element is set to nil after removal, confirming the fix.

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PR created automatically by Jules for task 13652935647002778501 started by @arran4

[google-labs-jules]

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[arran4]

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