Move asdate to CFTime and use timedecode in CommonDataModel

[felixcremer]

It seems that the asdate function here is conceptually doing the same as CFTime.decode with a slightly different interface.
Would it make sense to streamline this and move all date handling to CFTime?

This is coming from my struggle with opening a Zarr dataset with nanosecond units in CommonDataModel.

using Rasters
using Zarr
using ZarrDatasets
using Dates
using Downloads
using Mmap

testdatapath = Downloads.download("https://github.com/user-attachments/files/25968262/testdata.zip")
zstore = Zarr.ZipStore(Mmap.mmap(testdatapath))
z = zopen(zstore)
zdata = ZarrDataset(zstore)
 azimuth_time = CDM.cfvariable(zdata, :azimuth_time, prefer_datetime=false)
# This is wrong.

[Alexander-Barth]

for reference, this is what to be expected from xarray

In [7]: ds["azimuth_time"][0:3]
Out[7]: 
<xarray.DataArray 'azimuth_time' (azimuth_time: 3)> Size: 24B
array(['2025-06-26T05:34:21.819152000', '2025-06-26T05:34:21.820651861',
       '2025-06-26T05:34:21.822151722'], dtype='datetime64[ns]')


ds["azimuth_time"][-1]
# array('2025-06-26T05:34:21.967638284', dtype='datetime64[ns]')

Current released version:

using Zarr
using ZarrDatasets
using Dates
using Downloads
using CommonDataModel
using Mmap

testdatapath = Downloads.download("https://github.com/user-attachments/files/25968262/testdata.zip")
zstore = Zarr.ZipStore(Mmap.mmap(testdatapath))
z = zopen(zstore)
zdata = ZarrDataset(zstore)

CommonDataModel.cfvariable(zdata, :azimuth_time, prefer_datetime=false)[1:3]
# 3-element Vector{CFTime.DateTimeProlepticGregorian}:
# 2025-06-26T05:34:21.819152
# 2025-06-26T05:34:21.820152
# 2025-06-26T05:34:21.822152

CommonDataModel.cfvariable(zdata, :azimuth_time, prefer_datetime=false)[end]
# DateTimeProlepticGregorian(2025-06-26T05:34:21.967152)

[Alexander-Barth]

Should be fixed now.