ENH: Use NumberToString for lossless float metadata in MetaImage IO

Non-template MetaData fields of type double, float, vector<double>, and
Matrix<double> were serialized via std::ostringstream with default 6-digit
precision, silently truncating values with more than 6 significant digits.

Replace the lossy stream insertions with itk::ConvertNumberToString(),
which wraps Google double-conversion::ToShortest() and produces the
shortest decimal string that round-trips exactly through strtod/strtof.
Three call sites are affected:
- ExposeMetaData<double> / ExposeMetaData<float> in WriteImageInformation()
- ExposeMetaData<std::vector<double>> (manual loop replacing joinElements)
- WriteMatrixInMetaData<N>() template in the header

See: #3249

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

Author: hjmjohnson

Modules/IO/Meta/include/itkMetaImageIO.h

@@ -22,6 +22,7 @@
 
 #include <fstream>
 #include "itkImageIOBase.h"
+#include "itkNumberToString.h"
 #include "itkSingletonMacro.h"
 #include "itkMetaDataObject.h"
 #include "metaObject.h"
@@ -220,7 +221,7 @@ MetaImageIO::WriteMatrixInMetaData(std::ostringstream &       strs,
     {
       for (unsigned int j = 0; j < VNColumns; ++j)
       {
-        strs << mval[i][j];
+        strs << itk::ConvertNumberToString(mval[i][j]);
         if (i != VNRows - 1 || j != VNColumns - 1)
         {
           strs << ' ';

Modules/IO/Meta/src/itkMetaImageIO.cxx

@@ -21,6 +21,7 @@
 #include "itkIOCommon.h"
 #include "itksys/SystemTools.hxx"
 #include "itkMath.h"
+#include "itkNumberToString.h"
 #include "itkSingleton.h"
 #include "itkMakeUniqueForOverwrite.h"
 #include "metaImageUtils.h"
@@ -458,11 +459,11 @@ MetaImageIO::WriteImageInformation()
     }
     else if (ExposeMetaData<double>(metaDict, key, dval))
     {
-      strs << dval;
+      strs << itk::ConvertNumberToString(dval);
     }
     else if (ExposeMetaData<float>(metaDict, key, fval))
     {
-      strs << fval;
+      strs << itk::ConvertNumberToString(fval);
     }
     else if (ExposeMetaData<long>(metaDict, key, lval))
     {
@@ -510,7 +511,14 @@ MetaImageIO::WriteImageInformation()
     }
     else if (ExposeMetaData<std::vector<double>>(metaDict, key, vval))
     {
-      joinElements(vval, ' ', strs);
+      for (size_t i = 0; i < vval.size(); ++i)
+      {
+        if (i > 0)
+        {
+          strs << ' ';
+        }
+        strs << itk::ConvertNumberToString(vval[i]);
+      }
     }
     else if (WriteMatrixInMetaData<1>(strs, metaDict, key) || WriteMatrixInMetaData<2>(strs, metaDict, key) ||
              WriteMatrixInMetaData<3>(strs, metaDict, key) || WriteMatrixInMetaData<4>(strs, metaDict, key) ||