When HDF5 is found via its CMake config file, the code previously hardcoded
the hdf5_cpp-static target. On distributions that ship only shared HDF5
(e.g. Fedora rawhide where the config file was added in a newer package),
this caused a link failure. Now checks for hdf5_cpp-static, hdf5_cpp-shared,
and hdf5::hdf5_cpp-shared in order, falling back to module-mode discovery.