ENH: Use ConvertNumberToString for voxel spacing in VoxBoCUB IO

m_Spacing[] values (double) were written to the CUB text header with
default stream precision (6 significant digits), silently truncating
sub-millimeter or high-precision spacing values.  Replace with
itk::ConvertNumberToString() for shortest-round-trip serialization.

See: #3249

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hjmjohnson

Modules/Nonunit/Review/src/itkVoxBoCUBImageIO.cxx

@@ -19,6 +19,7 @@
 #include "itkIOCommon.h"
 #include "itkMetaDataObject.h"
 #include "itkByteSwapper.h"
+#include "itkNumberToString.h"
 #include "itksys/SystemTools.hxx"
 #include <iostream>
 #include <sstream>
@@ -668,7 +669,8 @@ VoxBoCUBImageIO::WriteImageInformation()
          << std::endl;
 
   // Write the spacing
-  header << m_VB_SPACING << ":\t" << m_Spacing[0] << '\t' << m_Spacing[1] << '\t' << m_Spacing[2] << std::endl;
+  header << m_VB_SPACING << ":\t" << ConvertNumberToString(m_Spacing[0]) << '\t' << ConvertNumberToString(m_Spacing[1])
+         << '\t' << ConvertNumberToString(m_Spacing[2]) << std::endl;
 
   // Write the origin (have to convert to bytes)