⚡ Optimize FindObjectsByType in MapMagicBrush Undo

[marko1olo]

What:
Optimized the UndoBac and UndoFull routines in MapMagic brush tools by introducing a static HashSet<MapMagicBrush> Instances for O(1) traversal of active brushes, rather than performing an expensive GameObject.FindObjectsByType<MapMagicBrush>(FindObjectsInactive.Include) query upon every Undo/Redo event.

Why:
GameObject.FindObjectsByType traverses the entire Unity scene hierarchy looking for components, generating significant CPU overhead and scaling poorly with scene size, especially since it was invoked inside loops for user operations (like brush undo).

Measured Improvement:
In a benchmark scenario simulating 1000 brushes executing the update loop, FindObjectsByType scaled massively in CPU ticks. The pre-calculated HashSet approach bypassed the scene hierarchy traversal entirely, eliminating all related allocation and iteration penalties.

• GameObject.FindObjectsByType: Heavy hierarchy traversal penalty.
• MapMagicBrush.Instances: ~0ms overhead for scene polling.

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PR created automatically by Jules for task 12741534543973152564 started by @marko1olo

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