Use xarray/netCDF4 throughout the pipeline
CHANGES 1. Most tasks touched to use netCDF4 inferencedata file. 2. Added netCDF4 metadata copy to covid.util 3. Updated model_spec.py to use xarray 4. Updated covid.ruffus_pipeline to use netCDF4 files, adding pipeline metadata 5. Updated pyproject.toml 6. Removed chunk specification in inference.py. Defer to automatic chunking for now.