Add a reader for NWC SAF GEO HRW data

[pnuu]

This PR adds a reader for the High Resolution Winds data from NWC SAF GEO.

The data structure is very complex, and due to the unsupported compound data type can't be opened with xr.open_dataset(). Because there are 259 datasets, I've made the dataset definitions dynamic instead of putting them into the reader YAML. The code is in a separate file because the internal structure is completely different to the other NWC SAF GEO products (see the linked issue).

By default the file handler reads the datasets separately for each imaging channel. That is, the datasets are named wind_vis06_air_pressure, wind_hrvis_wind_speed, and so on. The prefix is the name of the channel within the files.

The user can also supply reader_kwargs={"merge_channels": True} to collect all the data together. In this case the datasets are named without the prefix, such as air_pressure, wind_speed, etc.

• Closes Reader for NWC SAF HRW (high resolution winds) data #3052
• Tests added
• Fully documented

[codecov]

Codecov Report

Attention: Patch coverage is 97.73756% with 5 lines in your changes missing coverage. Please review.

Project coverage is 96.13%. Comparing base (869e4fe) to head (b2c4dc9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
satpy/readers/nwcsaf_hrw_nc.py	96.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3070    +/-   ##
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  Coverage   96.13%   96.13%            
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  Files         383      385     +2     
  Lines       55688    55909   +221     
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+ Hits        53534    53750   +216     
- Misses       2154     2159     +5     

Flag	Coverage Δ
behaviourtests	3.87% <0.00%> (-0.02%)	⬇️
unittests	96.23% <97.73%> (+<0.01%)	⬆️

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[pnuu]

I reduced the number of data rows that were written to the test data. With the original 1234 data points it took 19 seconds to run the tests on my laptop. Increasing to 12345 the tests took 170 seconds and with the current 123 only 2 seconds.

[pnuu]

I'll have a look at adding a kwarg to merge the different channel observations, so the user could do something like

scn = Scene(reader="nwcsaf-geo", filenames=filenames, reader_kwargs={"merge_channels": True})
scn.load(["wind_speed", "wind_from_direction"])

instead of loading each of the channels (wind_vis06_wind_speed, wind_vis08_wind_speed, etc.) separately.

[pnuu]

Also some documentation added.

[coveralls]

Pull Request Test Coverage Report for Build 13564327912

Details

• 218 of 223 (97.76%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 96.243%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
satpy/readers/nwcsaf_hrw_nc.py	121	126	96.03%

Totals
Change from base Build 13543289700:	0.006%
Covered Lines:	53999
Relevant Lines:	56107

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💛 - Coveralls