🧪 test: add comprehensive unit tests for QuadTree.Insert

[johnstrand]

🎯 What:
Added missing unit tests for QuadTree<T>.Insert and associated operations (Query, Remove, Clear, Subdivide).

📊 Coverage:

• Insert bounds validation (rejecting out-of-bounds positions).
• Insert within bounds and at boundary boundaries.
• Subdivision when exceeding node capacity and distribution into quadrant children.
• Max depth limit behavior to prevent infinite recursion.
• Inserting multiple items at identical positions.
• Item removal from leaf nodes and subdivided child nodes.
• Spatial range and radius queries (AABB and point/radius).
• Tree clearance (Clear).

✨ Result:
QuadTree<T> stateful operations are thoroughly tested, ensuring high reliability and structural integrity.

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PR created automatically by Jules for task 16959631983279362776 started by @johnstrand

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