refactor(snap): widen snap_pts to f64 (world_offset removal P2)

WireModel/LocalWire/TruckEntity snap buffers and the producers/consumers
now carry snap candidates as DVec3 (offset_snap_pts, dimension/multileader
producers, block-cache transform, pick/xclip, snap module). Still
offset-relative, so behaviour is unchanged — this just lets the snap
transport survive the upcoming switch to absolute coordinates without an
extra f32 quantization. The snap module still resolves in f32 (as_vec3 at
entry), matching today's precision.

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

src/snap/mod.rs

@@ -528,7 +528,7 @@ impl Snapper {
                     SnapHint::Midpoint => SnapType::Midpoint,
                 };
                 if self.is_on(snap_type) {
-                    try_pt(world, snap_type);
+                    try_pt(world.as_vec3(), snap_type);
                 }
             }
         }