harmonize API, auto-build HDF5

• harmonize API with legacy non-MPI h5fortran
• auto-build recent HDF5-MPI if not found/working
• require CMake >= 3.19 for robustness

cpu_count: make single target

we don't run benchmarks on CI due to their stability/demands. If benchmarks enabled, also enable tests.

update benchmark API

correct benchmarks API to match v2.0 h5fortran-mpi

make cpu_count match the scivision/physical-cpu-count project. explicit include directories.

add scheduled runs of Windows oneAPI

work with or without MPI

can now serve as a drop-in replacement for h5fortran (original, non-MPI) as well as be used for HDF5-MPI collective operations.

unify with h5fortran

added numerous features to bring in sync with h5fortran (original non-MPI)

initial release

based on h5fortran, now including HDF5-MPI parallel read, write of datasets and attributes.

Nearly all of the object-oriented functionality from h5fortran is present in h5fortran-mpi.

A key distinction for user programs is h5fortran-mpi REQUIRES MPI to be linked in the user program, EVEN IF the program doesn't use HDF5-MPI.

At a future point, to fully merge h5fortran and h5fortran-mpi, we might consider a build-time way to remove the need to link MPI for HDF5/h5fortran programs not using HDF5-MPI.