Add fsspec support to li_l2_nc reader

[pnuu]

This PR adds remote reading support to li_l2_nc reader via fsspec.

The change in NetCDF4FileHandler.collect_cache_vars() for getting the attributes is that for h5netcdf backend the v.__dict__ returns (for longitude dataset as an example):

{'_parent_ref': <weakref at 0x7fb98d573420; to 'File' at 0x7fb98d1d54f0>, '_root_ref': <weakref at 0x7fb98d573420; to 'File' at 0x7fb98d1d54f0>, '_h5path': '/longitude', '_dimensions': ('flashes',), '_initialized': True}

instead of v.attrs

<class 'h5netcdf.attrs.Attributes'>
_FillValue: -32767
long_name: 'Longitude of flash'
units: 'degrees_east'
standard_name: 'longitude'
scale_factor: 0.0027
add_offset: 0.0

This could be wrapped in dict(v.attrs) but apparently this already work as dictionary so there's no need.

The change is needed for the coordinates to be handled properly by setting standard_name, scale and offset.

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.93%. Comparing base (ed751f8) to head (12854de).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2753   +/-   ##
=======================================
  Coverage   95.92%   95.93%           
=======================================
  Files         375      375           
  Lines       53167    53237   +70     
=======================================
+ Hits        51003    51075   +72     
+ Misses       2164     2162    -2     

Flag	Coverage Δ
behaviourtests	4.12% <0.00%> (-0.01%)	⬇️
unittests	96.03% <100.00%> (+<0.01%)	⬆️

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[mraspaud]

I'm not very familiar with this, but it feels like it deserves a test...

[pnuu]

I agree, but I have no idea how to test. We don't access any real files in the tests.

[mraspaud]

Maybe we then should add one test with a real file?

[pnuu]

I have an idea, lets see if I can complete it today.

[pnuu]

f1bc699 should cover the addition. Fails with the original and passes with the current implementation for h5netcdf backend (remote reading).

[djhoese]

Just curious, does the ValueError come from the variable[:]? Would it make more sense to have a try/except dedicated to just the array creation and then a single xr.DataArray(...) creation at the end (that uses the attrs and var_arr or whatever created from the previous try/excepts).

[pnuu]

Yes, that's it. I refactored as suggested and added a test for the scalar case in 12854de

[mraspaud]

LGTM!