final optimizations for advection, transpose and hdf_io on host backend

examples/taylor_green/taylor_green_monoscale.py

...backend/host/python/operator/directional/advection_dir.py

hysop/backend/host/python/operator/transpose.py

hysop/fields/cartesian_discrete_field.py

hysop/mesh/cartesian_mesh.py

hysop/operator/hdf_io.py