COMP: Build the VTK examples against ITK 5.4, ITK 6, and VTK 9

[hjmjohnson]

With LSTK_USE_VTK=ON the examples and visualization tools have not built since the ITK 5 SpatialObject refactoring, and CI never exercises that option. This replaces the VTK 8 era vtk_module_config() block with find_package(VTK 9 COMPONENTS ...), updates the examples to the ITK 5 SpatialObject API, and builds all five executables against ITK 6 and VTK 9.6. Closes #42. Rebased onto main after #61 merged; the first seven commits are separate by class of change, fixes first and the style change last, and the eighth bumps the ITK 5.4 CI action pin, and the ninth fixes an intermittent exit-time segfault in itkLesionSegmentationMethodTest1.

Commits

1. COMP: find VTK 9 and link the module library (top-level CMakeLists.txt only).
2. COMP: vtk_module_autoinit() for the five executables (two CMake files, one added line per target).
3. COMP: ITK 5 SpatialObject API in the examples (CLI.h, ViewImageSlicesAndSegmentationContours.cxx).
4. COMP: return nullptr for an Image::Pointer, and the missing <iostream>.
5. BUG: misspelled include guard #define, one line.
6. COMP: override on the two Execute() methods.
7. STYLE: clang-format of the progress reporter header (whitespace only).
8. COMP: ITKRemoteModuleBuildTestPackageAction @v5.4.6 to @v5.4.7 in both ITK 5.4 jobs (answers a review question on COMP: Build and test against ITK 5.4 and ITK 6 #61).
9. BUG: LesionSegmentationMethod and FeatureAggregator kept a ProgressAccumulator member whose SetMiniPipelineFilter(this) SmartPointer formed a reference cycle, so neither was ever destroyed. The leaked PoolMultiThreader kept the global ThreadPool alive past its globals' teardown, and a late-starting pool thread then read a null ThreadPoolGlobals (itkThreadPool.cxx:193). The accumulator is now created in the call that uses it. On Linux with an ASan+UBSan ITK at 5d31af3cfdf the test crashed in 69 of 3000 parallel runs before and in 0 of 6000 after.

Nothing outside these classes changed (CI workflow pin aside): the existing CMake text is kept as written and only the required lines are added.

What was wrong

• CMakeLists.txt defined its own vtk_module_config() that prefixed names with an undefined _target_prefix and never called find_package(VTK), so Examples/ and Utilities/Visualization/ targets received neither the module include directory nor any VTK:: target; the build failed at the first VTK header.
• Examples/LesionSegmentationCLI.h and Utilities/Visualization/ViewImageSlicesAndSegmentationContours.cxx used SpatialObjectPoint::GetPosition()/SetPosition() and GroupSpatialObject::GetNumberOfObjects()/GetObjects(), all removed in ITK 5 (GetPositionInObjectSpace, SetPositionInObjectSpace, GetNumberOfChildren, GetChildren).
• Examples/LesionSegmentation.cxx returned NULL as an Image::Pointer; LesionSurfaceExtraction.cxx used std::cerr without <iostream>; the progress-reporter header had a misspelled guard and virtual overrides without override.

Test plan

External-module build on macOS arm64 against ITK main (6.0) and VTK 9.6 with -DLSTK_USE_VTK=ON: configure succeeds, LesionSegmentation, ViewImageAndSegmentationSurface, ViewImageSlicesAndSegmentationContours, LesionSurfaceExtraction, and IsoSurfaceVolumeEstimation all build, and LesionSegmentation -h prints its MetaCommand usage. The default configuration (LSTK_USE_VTK=OFF) configures as before, which is what CI runs; every change is inside if(LSTK_USE_VTK) or in files only that option compiles. Not built against ITK 5.4 with VTK; the API names used exist in 5.4.