mixture of .nc and .nc4 suffixes in spack-stack/2.0.0 crtm-fix/3.1.2.0

[RussTreadon-NOAA]

15 coefficient files in spack-stack/2.0.0 crtm-fix/3.1.2.0 end with the suffix .nc4. The remaining 1714 netcdf coefficient files end with the suffix .nc.

For example, on Gaea C6 we have

1. module use /ncrc/proj/epic/spack-stack/c6/spack-stack-2.0.0/envs/ue-oneapi-2025.2.1/modules/Core
2. module load crtm-fix/3.1.2.0
3. echo $CRTM_FIX returns /contrib/spack-stack/spack-stack-2.0.0/envs/ue-oneapi-2025.2.1/install/none/none/crtm-fix-3.1.2.0-ipi7gdt/fix
4. cd $CRTM_FIX
5. ls *.nc4 | wc returns 15

AerosolCoeff.CMAQ.nc4
AerosolCoeff.GOCART-GEOS5.nc4
AerosolCoeff.NAAPS.nc4
AerosolCoeff.nc4
CloudCoeff.GFDLFV3.-109z-1.nc4
CloudCoeff.Thompson08.-109z-1.nc4
CloudCoeff.WSM6.-109z-1.nc4
CloudCoeff.WSM6.MieSphere.nc4
CloudCoeff.nc4
CloudCoeff_DDA_Moradi_2022.nc4
CloudCoeff_TAMU-07Sep2015.nc4
CloudCoeff_TAMU-11Sep2014.nc4
Nalli.IRwater.EmisCoeff.nc4
Nalli2.IRwater.EmisCoeff.nc4
WuSmith.IRwater.EmisCoeff.nc4

6. ls *.nc | wc returns 1759

We should use a consistent suffix for netcdf CRTM coefficient files. The preferred suffix is .nc. The following is from https://docs.unidata.ucar.edu/netcdf-c/current/faq.html

What convention should be used for the names of netCDF files?
NetCDF files should have the file name extension ".nc". The recommended extension for netCDF files was changed from ".cdf" to ".nc" in 1994 in order to avoid a clash with the NASA CDF file extension, and now it also avoids confusion with "Channel Definition Format" files.

The same mix of .nc4 and .nc files is found in Ursa's spack-stack/2.0.0 crtm-fix/3.1.2.0

This issue is also reported in spack-stack #1913