STYLE: Move iterator declaration to for ContourExtractor2DImageFilter

Reduced the scope of the local `inputIt` variable in `GenerateDataForLabels()`,
by moving its declaration into the _init-statement_ of its `for` loop. Following
C++ Core Guidelines, Jul 8, 2025 "Declare names in for-statement initializers
and conditions to limit scope",
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#res-cond

Removed the `inputIt.GoToBegin()` call, following pull request
#5736
commit f10bd8f
"STYLE: Remove GoToBegin() calls on ImageRegionIteratorWithIndex"

Author: N-Dekker

Modules/Filtering/Path/include/itkContourExtractor2DImageFilter.hxx

@@ -350,8 +350,7 @@ ContourExtractor2DImageFilter<TInputImage>::GenerateDataForLabels()
     }
     // We use ImageRegionConstIteratorWithIndex here instead of RegionRange because we want access to the GetIndex()
     // method.
-    ImageRegionConstIteratorWithIndex<TInputImage> inputIt{ input, inputRegion };
-    for (inputIt.GoToBegin(); !inputIt.IsAtEnd(); ++inputIt)
+    for (ImageRegionConstIteratorWithIndex<TInputImage> inputIt{ input, inputRegion }; !inputIt.IsAtEnd(); ++inputIt)
     {
       const auto &      index = inputIt.GetIndex();
       BoundingBoxType & bbox = labelBoundingBoxes[inputIt.Get()];