refactor(snap): producers emit f64 snap points (world_offset removal P3)

TruckEntity.snap_pts is now DVec3 and every entity producer builds snap
candidates straight from the acadrust f64 coordinates instead of casting
to f32 first (text, mtext, arc, circle, ellipse, point, shape, solid,
mline, mtext, attribute, tolerance, table, underlay, ole2frame, mesh,
multileader, dimension, block-cache). offset_snap_pts stays f64
throughout. Still offset-relative (inert) — but snap precision is no
longer capped at ~0.5 m by an early f32 cast, which fixes a latent
UTM-scale snap error and sets up the absolute-coordinate switch.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/entities/shape.rs

@@ -6,7 +6,6 @@
 // gives a rough indication of the glyph orientation.
 
 use acadrust::entities::Shape;
-use glam::Vec3;
 
 use crate::command::EntityTransform;
 use crate::entities::common::{edit_prop as edit, ro_prop as ro, square_grip};
@@ -63,7 +62,7 @@ impl TruckConvertible for Shape {
         let oz = self.insertion_point.z;
         let size = self.size.abs().max(0.5);
 
-        let snap_pt = Vec3::new(ox as f32, oy as f32, oz as f32);
+        let snap_pt = glam::DVec3::new(ox, oy, oz);
         let pts = shape_marker(
             ox,
             oy,