fix attribute errors in healda script

[nbren12]

there were several errors like this:

[~/workspace/earth2studio/examples] main:a93583c0 :(
$ python3 22_healda.py
Traceback (most recent call last):
  File "/home/nbrenowitz/workspace/earth2studio/examples/22_healda.py", line 230, in <module>
    field = da.sel(variable=var).data[0].get()  # [nlat, nlon] cupy -> numpy
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'numpy.ndarray' object has no attribute 'get'

Earth2Studio Pull Request

Description

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The CHANGELOG.md is up to date with these changes.
• An issue is linked to this pull request.
• Assess and address Greptile feedback (AI code review bot for guidance; use discretion, addressing all feedback is not required).

Dependencies

[greptile-apps]

Greptile Summary

This PR fixes a runtime AttributeError in the 22_healda.py example by replacing the CuPy-specific .data[0].get() pattern with xarray's .values[0] accessor, which transparently converts GPU (CuPy) or CPU (NumPy) arrays to NumPy — making the plotting and MAE computation code device-agnostic.

• Three locations are updated: the analysis field plot loop (line 230), the MAE computation loop (lines 277–282), and the difference field plot loop (line 296–329).
• The fix is correct and clean; .values is the idiomatic xarray way to obtain a NumPy array regardless of the underlying backend.
• Two unchanged lines (280 and 300) still use .data[0] for era5_interp, which is inconsistent with the updated pattern and worth aligning for robustness.

Confidence Score: 4/5

• Safe to merge — the fix is correct and resolves a real runtime error; only minor consistency improvements are suggested.
• The change is narrowly scoped to an example script, corrects a documented and reproducible bug, and uses the idiomatic xarray API. The two remaining .data[0] calls for era5_interp are low-risk in practice but slightly inconsistent with the rest of the updated code.
• No files require special attention beyond the minor .data[0] inconsistency on lines 280 and 300.

Important Files Changed

Filename	Overview
examples/22_healda.py	Fixes AttributeError by replacing .data[0].get() (CuPy-specific) with .values[0] (xarray, always returns NumPy); era5_interp still uses .data[0] on unchanged lines, which is a minor inconsistency.

_{Last reviewed commit: "fix attribute errors..."}