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