Fix handling of new Satpy writer return values

[djhoese]

This fixes #236 by only handling new Satpy return types. It's possible it works with old Satpy since trollflow2 is now directly using split_results from Satpy which should do the heavy lifting of "what did the writer return?".

I'm tempted to also adapt this to now use Delayed at all for the most performance, but I think this should have a discussion. For example, some of the writers (geotiff, simple_image, and even AWIPS tiled) will return a dask array where each chunk (usually 1) of the array is a Path or str of the filename that was saved on disk. Taking advantage of this could probably improve trollflow2 handling of generated files as they are created. For example, pass the filename Array object to map_blocks where the map_blocks function is the trigger for the rest of processing (moving the file to final storage).

The merge of this should be coordinated with #233.

• Closes callbacks fail with latest trollimage or satpy #236
• Tests added
• Tests passed
• Passes flake8 trollflow2
• Fully documented
• Add your name to AUTHORS.md if not there already

[djhoese]

CI failing still. Ok so apparently I need to test this with stable Satpy and make it work with old and new.

[djhoese]

Ok so this works with old Satpy and old trollimage. This also works with new Satpy (main) and new trollimage (1.27.0, released yesterday), BUT it does not work with old Satpy and new trollimage.

Oh, maybe I can handle this...

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.95%. Comparing base (d69a75e) to head (76683dc).
⚠️ Report is 40 commits behind head on main.

Files with missing lines	Patch %	Lines
trollflow2/plugins/__init__.py	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #237      +/-   ##
==========================================
- Coverage   95.92%   94.95%   -0.97%     
==========================================
  Files          14       14              
  Lines        3311     3309       -2     
==========================================
- Hits         3176     3142      -34     
- Misses        135      167      +32     

Flag	Coverage Δ
unittests	94.95% <95.83%> (-0.97%)	⬇️

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[mraspaud]

Looks great, thanks a lot for the quick response!