Revert: stop honoring BlockRecord.is_loaded for xref skip decision

Empirically the DWG \"loaded\" bit doesn't track AutoCAD's XREF Manager
\"Loaded\"/\"Unloaded\" state reliably:

  - File A: manager \"Loaded\", on-disk is_loaded = Some(true)
  - File B: manager \"Loaded\", on-disk is_loaded = Some(false)

Same UI state, opposite bit values, so we were incorrectly skipping
xrefs the user wants loaded. Drop the `is_loaded == Some(false)` skip
and auto-resolve every xref again. The OOM problem this was meant to
mitigate is now addressed by the frustum culler, so loading more
xrefs no longer threatens the GPU budget.

The `BlockRecord::is_loaded` field + acadrust patch stay in place so
we can revisit once we identify the actual on-disk representation of
XREF→Unload (likely an XREF dependency record or
ACAD_XREF_PANEL_DATA xrecord).

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

src/io/xref.rs

@@ -34,28 +34,25 @@ pub struct XrefInfo {
 ///
 /// Returns a list of [`XrefInfo`] describing each xref block found.
 pub fn resolve_xrefs(doc: &mut CadDocument, base_dir: &Path) -> Vec<XrefInfo> {
-    // Collect xref blocks: (name, raw_path, block_record_handle, is_loaded)
-    // is_loaded == Some(false) means the host DWG marked this xref Unloaded
-    // via XREF→Unload; respect that and skip reading the external file.
-    let xref_entries: Vec<(String, String, Handle, Option<bool>)> = doc
+    // Collect xref blocks: (name, raw_path, block_record_handle)
+    //
+    // Note: `BlockRecord::is_loaded` (the DWG R2000+ "loaded" bit) turned out
+    // to be unreliable as a signal of AutoCAD's Unload state — different
+    // files with xrefs the manager calls "Loaded" carry both `Some(true)`
+    // and `Some(false)` on disk. Until we identify the actual on-disk
+    // representation of XREF→Unload (likely in an XREF dependency record
+    // or ACAD_XREF_PANEL_DATA xrecord), we auto-resolve every xref and
+    // rely on frustum culling to keep the GPU bounded.
+    let xref_entries: Vec<(String, String, Handle)> = doc
         .block_records
         .iter()
         .filter(|br| (br.flags.is_xref || br.flags.is_xref_overlay) && !br.xref_path.is_empty())
-        .map(|br| (br.name.clone(), br.xref_path.clone(), br.handle, br.is_loaded))
+        .map(|br| (br.name.clone(), br.xref_path.clone(), br.handle))
         .collect();
 
     let mut result = Vec::new();
 
-    for (block_name, raw_path, br_handle, is_loaded) in xref_entries {
-        if is_loaded == Some(false) {
-            result.push(XrefInfo {
-                name: block_name,
-                path: raw_path,
-                status: XrefStatus::Unloaded,
-            });
-            continue;
-        }
-
+    for (block_name, raw_path, br_handle) in xref_entries {
         let resolved = resolve_path(&raw_path, base_dir);
 
         let status = match &resolved {