Introduce `Rectangle.place` to position rectangles dynamically within bounds using anchor points. Added a demo (`DemoRectanglePlace01`) showcasing a 10x10 grid of rectangles evenly distributed across the canvas.
This commit introduces `Rectangle.irregularGrid`, enabling the creation of grids with irregular spacing based on weights. New helper methods and properties for 2D rectangle lists, such as subgrid selection, bounds calculation, and random access, are also added. Additionally, two new demos showcase regular and irregular grid features.
