Preserve Xarray legacy compat and join behaviors

[tomvothecoder]

Description

• Closes [DevOps] Preserve Xarray's legacy compat and join behaviors and address FutureWarning #798

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

If applicable:

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass with my changes (locally and CI/CD build)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)

[tomvothecoder]

Hey @jasonb5 can you do a quick review of this PR? I highlighted the changes in my self-review below. The existing test build passes.

I want to get this in before the next release (next two weeks). Thanks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (92b3d2e) to head (037e05a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #800   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           16        16           
  Lines         1782      1784    +2     
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+ Hits          1782      1784    +2     

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[jasonb5]

LGTM
Just one thing, if None is False do we need to allow None for use_new_combine_kwargs_defaults?

[tomvothecoder]

Thanks for the review @jasonb5.

LGTM Just one thing, if None is False do we need to allow None for use_new_combine_kwargs_defaults?

I actually removed use_new_combine_kwarg_defaults since I think it is a temporary placeholder (here 23a3eb2).

I realized that it is redundant to set compat/join explicitly while setting use_new_combine_kwargs_defaults. Both methods silence the FutureWarning.

[Copilot]

Pull Request Overview

Preserve legacy Xarray merge/alignment behavior in xcdat.open_mfdataset by default, aligning with pre-Xarray-0.23 defaults.

• Add compat and join keyword-only parameters with legacy defaults ("no_conflicts" and "outer") and forward them to xr.open_mfdataset
• Update documentation to explain the preserved defaults and options
• Adjust tests’ expectations to reflect legacy compat/join defaults

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
xcdat/dataset.py	Adds compat and join parameters and forwards them via kwargs to xr.open_mfdataset; updates docstrings.
tests/test_dataset.py	Updates expected merges in tests to use compat="no_conflicts" and join="outer".

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[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

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