2D geometry primitives for the Stipple UI toolkit.
Stipple works in logical pixels (f64): device-independent units that
the platform layer converts to physical device pixels using a
[ScaleFactor]. All layout, hit-testing, and the public widget API speak
logical pixels; physical pixels appear only at the stipple-platform /
stipple-render boundary (see [PhysicalSize]).
This crate is a dependency-free leaf. Interop with oxideav-core's
Transform2D lives in stipple-render, at the render boundary, to keep the
geometry types free of any rendering dependency.