crossrefitem: fix SIGSEGV crash + improve double-click navigation + fix PDF/SVG/print rendering

Fix a use-after-free crash (SIGSEGV in QRegion::begin, Qt5Gui+0x49af60)
confirmed by analysis of 19 coredumps. The crash was triggered when the
scene viewport clip region was freed during zoom/resize events while
QPicture::play() replayed drawPolyline commands through the scene painter.
Qt's raster engine then dereferenced a stale QRegionData pointer.

Root cause: CrossRefItem used three nested QPicture objects (m_drawing,
m_hdr_no_ctc, m_hdr_nc_ctc). The nested drawPicture() calls amplified
the use-after-free risk on any repaint event.

Fix: remove all QPicture from CrossRefItem entirely.
- updateLabel() now uses a QImage-backed dummy painter to compute
  m_bounding_rect, m_shape_path and m_hovered_contacts_map geometry.
  A bool m_update_map flag prevents the map from being overwritten
  during paint().
- paint() calls drawAsCross()/drawAsContacts() directly on the scene
  painter — no QPicture::play() anywhere in the class.
- buildHeaderContact() now draws NO/NC symbols directly onto the painter
  instead of recording them into QPicture members.

Also fix mouseDoubleClickEvent: the element under the click is now found
directly from m_hovered_contacts_map using the event position, rather
than relying on m_hovered_contact which could be reset by hoverMoveEvent
between the two clicks of a double-click.

Also remove setBold(true) on terminal name labels: the Qt PDF/SVG/print
engine rendered bold at 4pt as extremely thick glyphs, making exports
unreadable. Normal weight at 4pt is correct and legible on all backends.

Fixes: SIGSEGV in CrossRefItem::paint() on zoom/resize
Fixes: double-click navigation unreliable on Xref contact symbols
Fixes: terminal name labels unreadable in PDF/SVG/print export

sources/qetgraphicsitem/crossrefitem.h

@@ -22,7 +22,6 @@
 
 #include <QGraphicsObject>
 #include <QMultiMap>
-#include <QPicture>
 
 class Element;
 class DynamicElementTextItem;
@@ -103,7 +102,7 @@ class CrossRefItem : public QGraphicsObject
 
 	private:
 		void linkedChanged();
-		void buildHeaderContact();
+		void buildHeaderContact(QPainter &painter, QPointF no_pos, QPointF nc_pos);
 		void setUpCrossBoundingRect(QPainter &painter);
 		void drawAsCross(QPainter &painter);
 		void drawAsContacts(QPainter &painter);
@@ -117,10 +116,10 @@ class CrossRefItem : public QGraphicsObject
 	private:
 		Element *m_element; //element to display the cross reference
 		QRectF m_bounding_rect;
-		QPicture m_drawing, m_hdr_no_ctc, m_hdr_nc_ctc;
 		QPainterPath m_shape_path;
 		XRefProperties m_properties;
 		int m_drawed_contacts;
+		bool m_update_map = false;
 		QMultiMap <Element *, QRectF> m_hovered_contacts_map;
 		Element *m_hovered_contact = nullptr;
 		DynamicElementTextItem *m_text = nullptr;