write a single grib file that is globally valid

[sanAkel]

This PR resolves: #91

What does it provide?

In response to what is needed it provides scripts to:

Input global netcdf with surface fields.
Write corresponding global grib file.

And it is agnostic to the source of netcdf file, i.e., the python script does not care if the netcdf file is an
output from the UFS/MOM and CICE or RTOFS v2.5 (archive converted to nc).

@DanIredell-NOAA Please:

• Make sure these listed steps work for you as well.
• Once confirmed, please integrate into the workflow with an option, default False, and once approved by @yangfanglin we can set it to True and set all regional grib2 processing with CDO False. 🙏

Proof that it worked

santha.akella@dlogin03:~/large_fs/nc2grib_issue_91> ./run_nc2grib.sh 
Detected Grid: IMAX=4500, JMAX=3298
Step 2: Encoding to GRIB2...
 lengrib returned from gribend=    15290258
 Return code from baclose=           0
----------------------------------------------
Success! GRIB2 file created: rtofs_output.grb2

santha.akella@dlogin03:~/large_fs/nc2grib_issue_91> ls -alt
total 146760
-rw-r--r-- 1 santha.akella couple  15290258 Dec 27 23:46 rtofs_output.grb2
drwxr-sr-x 4 santha.akella couple      4096 Dec 27 23:45 .
-rw-r--r-- 1 santha.akella couple         4 Dec 27 23:45 fort.30
...
...

Grib2 file is valid!

wgrib2 -v rtofs_output.grb2 
1:0:d=2025122712:WTMP Water Temperature [K]:0 m below sea level:anl: