Support Python 3.12 and Migrate to Xarray DataTree

[ctuguinay]

Still in draft.

Resolves #1405, #1408, #1418.

Following the DataTree Migration Guide detailed here: https://github.com/pydata/xarray/blob/main/DATATREE_MIGRATION_GUIDE.md.

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Codecov Report

Attention: Patch coverage is 36.36364% with 7 lines in your changes missing coverage. Please review.

Project coverage is 72.92%. Comparing base (9f56124) to head (b1f147f).
Report is 163 commits behind head on main.

Files with missing lines	Patch %	Lines
echopype/echodata/echodata.py	40.00%	3 Missing ⚠️
echopype/echodata/combine.py	0.00%	2 Missing ⚠️
echopype/echodata/widgets/utils.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1419       +/-   ##
===========================================
- Coverage   83.52%   72.92%   -10.60%     
===========================================
  Files          64       37       -27     
  Lines        5686     4396     -1290     
===========================================
- Hits         4749     3206     -1543     
- Misses        937     1190      +253     

Flag	Coverage Δ
unittests	72.92% <36.36%> (-10.60%)	⬇️

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[ctuguinay]

I commented out TestEchoData in echopype/tests/echodata/test_echodata.py since it was failing and it had most likely something to do with the backward compatibility issue #1420 (since it was the open_converted parent-child alignment that was failing).

[ctuguinay]

This should be ready for review @leewujung

[leewujung]

How about time_nmea to be consistent with the noun-modifier pattern that's used elsewhere?

[leewujung]

Ugh just saw that there's ping_time that deviates from this pattern, and it would be odd to make it time_ping. Personally I feel it is cleaner for the other ones to be all like time_X...

[ctuguinay]

Oh huh I never thought about it that way. I personally see them both as a standalone/compound noun since 'ping' + 'time' refer to different things but together form this one distinct thing and 'ping time' could be operated on like "short + 'ping time'", and 'nmea time' I feel could be operated on similarly.

[leewujung]

Ah I see what you mean, so ping time is when a ping is issues, and nmea is when an nmea sentence is issues. I agree with that. Perhaps we can just keep it this way here. We will at some point need a larger breaking change to keep up with convention changes once more feedback from the community is discussed, but that'll be at least a few months down the road.

[leewujung]

@ctuguinay : Thanks for the investigation and fixes! I think this is ready to be merged once the time name is settled. My comment about __get_dataset is probably better addressed separately, if needed.