perf: Fix all clazy qstring-allocation warnings (#903)

src/lib_gui/qt/view/QtGraphViewStyleImpl.cpp

@@ -9,7 +9,7 @@
 float QtGraphViewStyleImpl::getCharWidth(const std::string& fontName, size_t fontSize)
 {
 	return QFontMetrics(getFontForStyleType(fontName, fontSize))
-			   .width("QtGraphNode::QtGraphNode::QtGraphNode") /
+			   .width(QStringLiteral("QtGraphNode::QtGraphNode::QtGraphNode")) /
 		37.0f;
 }