Fix the handling of AMVs unit to units by applying suggestion in #2898

[YouvaEUMex]

As describved in #2898, the AMV datasets returned by the fci_l2_nc reader contain the attribute unit, rather than units, which is the CF naming convention. This is an inherited issues since the FCI L2 NetCDF files use the unit attribute, which is then read and used by the reader.

This PR apply the work around developed for other FCI L2 product file handler to the AMVs.

To that extend it slightly refactor FciL2CommonFunctions._set_attributes to handle the AMVs product (not pixels nor segmented) and change slightly the interface to the segmented( that is also changed in the dedicated get_dataset)

The changes are already described in #2898

• Closes units attribute is not CF conform for the for AMV datasets in the fci_l2_nc reader  #2898

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.11%. Comparing base (0b9760c) to head (d42c00d).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3031      +/-   ##
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- Coverage   96.12%   96.11%   -0.02%     
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  Files         383      383              
  Lines       55577    55577              
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- Hits        53424    53416       -8     
- Misses       2153     2161       +8     

Flag	Coverage Δ
behaviourtests	3.91% <0.00%> (ø)
unittests	96.20% <100.00%> (-0.02%)	⬇️

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[coveralls]

Pull Request Test Coverage Report for Build 12793012035

Details

• 15 of 15 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.217%

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Totals
Change from base Build 12766191418:	0.0%
Covered Lines:	53664
Relevant Lines:	55774

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💛 - Coveralls

[strandgren]

Thanks for this @YouvaEUMex. I've left one comment in line. I would also suggest removing the _get_global_attributes method in FciL2NCAMVFileHandler and instead add a check in the corresponding method in FciL2CommonFunctions to add the channel information in case of reading AMV data.

I

[strandgren]

I suggest three minor changes on the updated code.