chore: clear dead-code and unused-import warnings

Remove the unused `crate::par::prelude` glob import in wire_gpu.rs and
the never-called `viewport_at_paper_point` method; fold its doc into the
screen-space twin that is actually used so no intra-doc link dangles.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/pipeline/wire_gpu.rs

@@ -27,8 +27,6 @@
 
 use crate::scene::model::wire_model::WireModel;
 use iced::wgpu;
-#[cfg(not(target_arch = "wasm32"))]
-use crate::par::prelude::*;
 
 /// Allocate a VERTEX buffer with `mapped_at_creation` and write `data` directly
 /// into the mapped slice. Skips the intermediate staging copy that