feat(xref): honor BlockRecord is_loaded — skip Unloaded xrefs

When the host DWG marks an xref as Unloaded (via XREF→Unload in
AutoCAD), the user explicitly chose NOT to load that reference. We
were ignoring that and pulling the external file in anyway, which
on large drawings could push GPU memory past the device budget.

Bump the acadrust dep to the branch that exposes
`BlockRecord::is_loaded`, then short-circuit `resolve_xrefs` for
any entry with `is_loaded == Some(false)`. New `XrefStatus::Unloaded`
surfaces this in the command-line log so the user can see which
references were skipped (and can re-load them via the XREF dialog).

Co-Authored-By: Claude Opus 4.7 <[email protected]>

Cargo.lock

@@ -41,7 +41,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.3.4"
-source = "git+https://github.com/HakanSeven12/acadrust?rev=622729f#622729f961dae4d29fbc890d3622a3a86294ec8d"
+source = "git+https://github.com/HakanSeven12/acadrust?branch=feat%2Fexpose-blockrecord-is-loaded#44ee57604af6f29a3f3ace05c2e49879fb8ae18a"
 dependencies = [
  "ahash",
  "anyhow",