Fix Qt6 nodiscard warnings for QtConcurrent::run

- Add (void) cast to QtConcurrent::run calls in base_symbol_model.cpp
- Suppresses Qt6 nodiscard warnings for unused QFuture return values
- Applies to 3 locations where QFuture is used for async callback pattern

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/Lts/Viewer/SituationMap/SymbologyImpl/base_symbol_model.cpp

@@ -228,7 +228,7 @@ QImage BaseSymbolItem::getSearchSwatch()
     m_esriSearch.m_swatchFuture = m_esriSearch.m_esriSymbol->createSwatchAsync(SWATCH_SIZE, SWATCH_SIZE, 1);
     
     // Use QtConcurrent to handle completion
-    QtConcurrent::run([this, future = m_esriSearch.m_swatchFuture]() mutable {
+    (void)QtConcurrent::run([this, future = m_esriSearch.m_swatchFuture]() mutable {
       future.waitForFinished();
       if (future.isFinished() && !future.isCanceled()) {
         QImage image = future.result();
@@ -276,7 +276,7 @@ QImage BaseSymbolItem::getFetchSwatch()
     // Qt6: Use QFuture pattern instead of signals
     m_esriFetch.m_symbolFuture = m_esriDictionary->fetchSymbolAsync(keys, this);
     
-    QtConcurrent::run([this, future = m_esriFetch.m_symbolFuture]() mutable {
+    (void)QtConcurrent::run([this, future = m_esriFetch.m_symbolFuture]() mutable {
       future.waitForFinished();
       if (future.isFinished() && !future.isCanceled()) {
         Esri::ArcGISRuntime::Symbol *symbol = future.result();
@@ -298,7 +298,7 @@ void BaseSymbolItem::onEsriFetchCompleted(Esri::ArcGISRuntime::Symbol *symbol)
   // Qt6: Use QFuture pattern instead of signals
   m_esriFetch.m_swatchFuture = m_esriFetch.m_esriSymbol->createSwatchAsync(SWATCH_SIZE, SWATCH_SIZE, 1);
   
-  QtConcurrent::run([this, future = m_esriFetch.m_swatchFuture]() mutable {
+  (void)QtConcurrent::run([this, future = m_esriFetch.m_swatchFuture]() mutable {
     future.waitForFinished();
     if (future.isFinished() && !future.isCanceled()) {
       QImage image = future.result();