feat: default timespan

[pgierz]

Closes #171

Still needs to be tested (for now manually), and I have no idea how to write tests for this...

[pgierz]

Many of the changes in this PR are cosmetic, I have commented the important parts.

[pgierz]

Seems to work with the basic example from the workshop. After specifying nothing at all in the user config file, you can see in the log that it will try to use 1YS as a file timespan:

Processing basic.yaml
...
ENABLE_DASK: 'yes'
ENABLE_FLOX: 'yes'
ENABLE_OUTPUT_SUBDIRS: 'no'
FILE_TIMESPAN: 1YS
PARALLEL: 'yes'
PARALLEL_BACKEND: dask
...

The produced files also seem to have correct timestamps:

❯ ls
basic.yaml          tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185001-185012.nc  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185501-185512.nc
logs                tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185101-185112.nc  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185601-185612.nc
pymor-basic.slurm   tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185201-185212.nc  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185701-185712.nc
pymor_report.log    tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185301-185312.nc  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185801-185812.nc
slurm-17386524.out  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185401-185412.nc  tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185901-185912.nc

Also internally:

❯ ncdump -h tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185001-185012.nc
netcdf tas_Amon_AWI-AWI-CM-1-1-HR_piControl_r1i1p1f1_gn_185001-185012 {
dimensions:
        time = UNLIMITED ; // (12 currently)
        lat = 360 ;
        lon = 720 ;
variables:
        double lat(lat) ;
                lat:_FillValue = NaN ;
        double lon(lon) ;
                lon:_FillValue = NaN ;
        double time(time) ;
                time:standard_name = "time" ;
                time:long_name = "time" ;
                time:axis = "T" ;
                time:units = "days since 1850-01-01 00:00:00.000000" ;
data:

 time = 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 ;
}

Can be reviewed. If anyone wants to try inventing unit tests, please :-)

[pgierz]

@JanStreffing, I also added you as reviewer since it was your feature request. If you want to try this out, get the branch feat/default_timespan and try re-running some of the workshop examples.