Fixes preserving ds/da attributes in the regrid2 module

[jasonb5]

Description

Fixes preserving the DataArray attributes when regridding using the regrid2 module.

• Closes [Bug]: Regrid does not preserve attributes #445

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)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (d86a116) 100.00% compared to head (cb48817) 100.00%.

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Additional details and impacted files

@@            Coverage Diff            @@
##              main      #468   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           14        14           
  Lines         1424      1424           
=========================================
  Hits          1424      1424           

Impacted Files	Coverage Δ
xcdat/regridder/regrid2.py	100.00% <ø> (ø)

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[lee1043]

@jasonb5 thank you for the PR. I confirm this resolves #445.

>>> import xcdat as xc
>>> ds = xc.open_dataset('/work/lee1043/cdat/pmp/E3SM/E3SMv3_evaluation/mean_climate/clim/cmip6.historical.E3SMv3.r1i1p1f1.mon.pr.198101-200512.AC.v20230404.nc')
>>> ds['pr'].units
'kg m-2 s-1'
>>> t_grid = xc.create_uniform_grid(-88.875, 88.625, 2.5, 0, 357.5, 2.5)
>>> varname = 'pr'
>>> ds_regridded = ds.regridder.horizontal(varname, t_grid, tool='regrid2')
>>> ds_regridded[varname].attrs
{'standard_name': 'precipitation_flux', 'long_name': 'Precipitation', 'comment': 'includes both liquid and solid phases', 'units': 'kg m-2 s-1', 'cell_methods': 'area: time: mean', 'cell_measures': 'area: areacella', 'operation': 'temporal_avg', 'mode': 'climatology', 'freq': 'month', 'weighted': 'True'}
>>> ds_regridded['pr'].units
'kg m-2 s-1'

[tomvothecoder]

LGTM

[lee1043]

Can we merge this?