DWF and DGN underlays: attach, display, snaps, frames and references

DWFATTACH / -DWFATTACH and DGNATTACH / -DGNATTACH attach a DWF / DWFx sheet
or a DGN (V7 or V8) model with the reference's prompts; ATTACH routes the
file types to them. The sheet or model is read into vector paths, drawn as a
transparent underlay raster (contrast, fade, monochrome and background
adjustment apply) and offers its geometry to object snaps. Definitions are
kept in ACAD_DWFDEFINITIONS / ACAD_DGNDEFINITIONS, the External References
palette lists and reloads them, and image textures get line-keeping mip
levels so thin underlay lines stay visible when zoomed out.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

Cargo.toml

@@ -42,6 +42,10 @@ flate2 = "1"
 image = { version = "0.25", default-features = false, features = ["png", "jpeg", "bmp", "tiff"] }
 hayro = "0.7.1"
 kurbo = "0.13"
+# DWF/DWFx packages, their XPS pages and DWF/DGN underlay rasters.
+zip = { version = "8", default-features = false, features = ["deflate"] }
+roxmltree = "0.20"
+tiny-skia = "0.11"
 # Rasterises assets/logo.svg into the window icon at startup, so the taskbar
 # icon comes from the same file every other build target does. Already in the
 # tree behind iced's svg feature; named here only to use it directly.