Replace netcdf-fortran with a FORCES-owned netcdf-c wrapper

This merge request removes the netcdf-fortran dependency from FORCES and replaces it with a FORCES-owned wrapper built directly on top of netcdf-c.

The new wrapper is implemented in mo_netcdf_wrapper and provides the NetCDF-4 subset currently needed by FORCES. Existing higher-level FORCES interfaces such as mo_netcdf, mo_ncread, and mo_ncwrite now use that wrapper instead of importing netcdf-fortran.

Motivation

The main motivation for this change is to avoid recurring problems caused by netcdf-fortran, in particular:

• fragile compiler-dependent behavior in the Fortran bindings
• packaging and compatibility issues around netcdf-fortran
• the problematic FourByteInt handling in netcdf-fortran, which can create unnecessary flat copies for large integer(i4) arrays
• dimension sizes limited by default integers

By switching to a thin FORCES-owned wrapper around netcdf-c, we keep control over the supported API surface, numeric kinds, and data-path behavior.

Main Changes

• Added mo_netcdf_wrapper as a strict-kind NetCDF wrapper on top of netcdf-c
• Added a small C companion layer for stable access to selected netcdf-c functionality
• Refactored mo_netcdf, mo_ncread, and mo_ncwrite to use the new wrapper instead of netcdf-fortran
• Kept the existing FORCES OOP NetCDF API in mo_netcdf intact for current callers
• Preserved FORCES NetCDF semantics at the wrapper boundary:
  • Fortran-style 1-based slicing indices
  • current FORCES dimension ordering
  • strict use of mo_kind / iso_c_binding kinds inside the wrapper
• Kept the direct-buffer integer(i4) I/O path so contiguous i4 reads and writes do not go through the problematic flat-copy behavior
• Added wrapper support for small but useful nf90-style file and metadata routines such as:
  • redef, abort
  • inq_path, inq_format
  • attribute copy/delete
  • group rename
  • variable-property inquiry and fill handling
• Added a dedicated mo_netcdf_wrapper pfUnit test module
• Added documentation of the remaining interface gaps compared to netcdf-fortran

Compatibility

• No intended breaking changes for existing FORCES users of mo_netcdf
• Production code under src/ no longer imports netcdf
• The wrapper is intentionally a FORCES-owned NetCDF-4 subset, not a full replacement for the entire netcdf-fortran surface
• Parallel NetCDF I/O via MPI is still out of scope
• Concurrent OpenMP threads calling NetCDF routines directly are still not supported by this change

Validation

The following areas were validated:

• build with NetCDF C only
• no use netcdf remaining in production sources
• existing NetCDF-related pfUnit suites
• dedicated wrapper regressions for:
  • inq_path / inq_format
  • redef / enddef / abort
  • attribute copy/delete
  • group rename
  • variable-property inquiry
  • fill-value define/inquire

Notes

• This merge request does not try to expose the full netcdf-fortran API.
• The wrapper preserves familiar nf90-style behavior where useful, but it is an independent FORCES implementation built on netcdf-c.