NotImplementedError: Only linear polarizations are supported, requested polarization=LV

In running the NEN7_NISAR coordinated dataset (https://wiki.jpl.nasa.gov/display/NISARSDS/Case+11a%3A+NEN7_NISAR+Coordinated+Dataset) through R4.0.1 PCM (R4.0.1 PGE + ISCE3 0.19.2+32e2d2dd0), we encountered a failed RSLC job with the following traceback:

2024-02-14 10:12:16.144, INFO, RSLC, focus, 999999, /opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py:1150, "Normalizing chirp to unit white noise gain."
2024-02-14 10:12:16.144, INFO, RSLC, focus, 999999, /opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py:1171, "Renormalizing chirp by signal gain terms wavelength * PRF * sqrt(TBP) = 25346.47469541087"
journal: cube height: 20
journal:
 -- cube length: 168
 -- cube width: 317
journal: EPSG: 4326
Traceback (most recent call last):
  File "/opt/conda/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/opt/conda/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py", line 1664, in <module>
    main(sys.argv[1:])
  File "/opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py", line 1660, in main
    focus(cfg, args.run_config_path)
  File "/opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py", line 1546, in focus
    rc, rc_grid, shift, deramp_rc = prep_rangecomp(cfg, raw, raw_grid,
  File "/opt/conda/lib/python3.9/site-packages/nisar/workflows/focus.py", line 1176, in prep_rangecomp
    scale, delay = get_scale_and_delay(cal, channel_in.pol)
  File "/opt/conda/lib/python3.9/site-packages/nisar/products/readers/rslc_cal.py", line 243, in get_scale_and_delay
    raise NotImplementedError("Only linear polarizations are supported, "
NotImplementedError: Only linear polarizations are supported, requested polarization=LV
2024-02-14T10:12:18.664030Z, Error, PGE::rslc_l_pge.py, run_sas_program, 303004, /opt/pge/l1_l2/sas_runner.py:79, "SAS program failed with exit code 1"

Per @bhawkins-jpl, the SAS needs work to support circular pol.

The runconfig and all inputs to the job can be downloaded from s3://nisar-dev/test/for_brian/only_linear_pols_supported/.

Start with nisar/products/readers/rslc_cal.py, especially get_scale_and_delay, and trace its call from nisar/workflows/focus.py in prep_rangecomp. Reproduce the failure using the runconfig and inputs in s3://nisar-dev/test/for_brian/only_linear_pols_supported/. Done means the RSLC workflow handles the requested LV circular polarization without raising the reported NotImplementedError.