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/ifcviewer/GeometryStreamer.h

@@ -41,7 +41,6 @@ struct ElementInfo {
     std::string guid;
     std::string name;
     std::string type;
-    int parent_id;
 };
 
 class GeometryStreamer : public QObject {
@@ -70,8 +69,8 @@ public:
 
 signals:
     void progressChanged(int percent);
-    void meshReady(MeshChunk chunk);
-    void instanceReady(InstanceChunk chunk);
+    void meshReady(StreamedMesh mesh);
+    void instanceReady(StreamedInstance instance_record);
     void finished();
     void cancelled();
     void errorOccurred(const QString& message);