Support for uint64_t in Xdmf/HDF5

Hello,

I’m using Xdmf/hdf5 data format and noticed that 64 bits unsigned integer are not properly supported

Can someone review the modifications and/or tell me what is the proper way of bringing uint64 to xdmf ?
Thank you

Closing the loop, I believe this has been resolved via https://gitlab.kitware.com/vtk/vtk/-/merge_requests/10726.