Prototype an R-tree for SegmentPad #633
Description
An R-tree is a spatial index allowing fast search for geometry entities. We will need the spatial indices for points, line segments, Bezier curves, and more geometry entities to be included in modmesh.
This issue is to track the first, prototype-ish implementation of R-tree for the line segments in SegmentPad. The spatial index will be a foundation for high-level features.
The R-tree implementation should allow both 2 and 3 dimensional entities, but the tests can focus on 2D at the moment.