ifcviewer: rename sidecar transfer/record types; drop unused element hierarchy (sidecar v17)

Rename the streamer/sidecar transfer and record types to describe what
they are rather than how they move:

  MeshChunk         -> StreamedMesh
  InstanceChunk     -> StreamedInstance
  InstanceCpu       -> InstanceInfo
  PackedElementInfo -> ElementTableRecord
  uploadMeshChunk   -> uploadStreamedMesh
  uploadInstanceChunk -> uploadStreamedInstance
  buildMeshChunk    -> buildStreamedMesh

and the two post-index sidecar metadata blocks:

  "critical" metadata -> "geometry" metadata  (meshes/instances/georef/TOC)
  "deferred" metadata -> "element"  metadata  (elements + string table)
  parseSidecarCritical -> parseSidecarGeometryMetadata
  parseSidecarDeferred -> parseSidecarElementMetadata

The one behavioural change: the element hierarchy (parent_id) was
carried through ElementInfo, ElementTableRecord, and the sidecar element
table but never consumed, so drop it and bump SIDECAR_VERSION 16 -> 17.
No back-compat: regenerate sidecars. sample.ifcview is regenerated at v17.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/bonsaiviewer/ElementRegistry.h

@@ -30,7 +30,7 @@
 #include <vector>
 
 class SceneLoader;
-struct PackedElementInfo;
+struct ElementTableRecord;
 struct ElementInfo;
 
 namespace bonsaiviewer {
@@ -39,7 +39,6 @@ struct BasicElementInfo {
     uint32_t object_id = 0;
     uint32_t model_id = 0;
     int ifc_id = 0;
-    int parent_id = 0;
     QString guid;
     QString name;
     QString type;
@@ -59,7 +58,7 @@ public:
 
 private:
     void onSidecarElementsReady(uint32_t model_id,
-                                std::vector<PackedElementInfo> elements,
+                                std::vector<ElementTableRecord> elements,
                                 std::string string_table);
     void onStreamedElementsReady(uint32_t model_id, std::vector<ElementInfo> elements);