Fix background_deviation_box discarding the xpx.at result on immutable backends

[mwcraig]

background_deviation_box called xpx.at(barr)[y1:y2, x1:x2].set(...) without rebinding the result. xpx.at(...).set() returns a new array, so on immutable backends (JAX, array-api-strict) every box was silently left at the global standard deviation. This rebinds the result.

The existing test_background_deviation_box only checked the mean of the output, which happens to pass on JAX even when the per-box values are never written. A new regression test (test_background_deviation_box_per_box_values) uses different noise scales in different boxes and checks the per-box values; it fails on JAX before the fix and passes after. The existing test now uses xp.mean() so it also runs on array-api-strict.

Test matrix (full suite unless noted):

backend	result
numpy	381 passed, 5 skipped
jax	367 passed, 10 skipped, 2 xfailed, 7 xpassed (all 7 XPASS are pre-existing combiner / image_collection entries)
dask	371 passed, 15 skipped
array-api-strict, test_cosmicray.py only	before: 1 failed, 7 passed, 33 xfailed; after: 9 passed, 33 xfailed

Fixes #963

🤖 Generated with Claude Code

https://claude.ai/code/session_01DTN9DnPnLKK2u7knnMJ2gA

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.83%. Comparing base (89e90f9) to head (e3053e4).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #977   +/-   ##
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  Coverage   95.83%   95.83%           
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  Files           8        8           
  Lines        1631     1631           
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  Hits         1563     1563           
  Misses         68       68           

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[Copilot]

Pull request overview

Fixes background_deviation_box for immutable Array API backends (e.g., JAX) by correctly rebinding the result of a functional array update, and strengthens regression coverage to ensure per-box values are actually written.

Changes:

• Rebind xpx.at(...).set(...) result in background_deviation_box so updates take effect on immutable backends.
• Improve/extend tests to validate per-box deviations (and adjust existing mean check to be Array API compatible).
• Add a changelog entry describing the bug and fix.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
ccdproc/core.py	Rebinds functional update result to make per-box writes effective on immutable backends.
ccdproc/tests/test_cosmicray.py	Updates existing test for backend compatibility and adds per-box regression test for #963.
CHANGES.rst	Documents the bug fix in the unreleased changelog.
ccdproc/__init__.py	Adds a blank line after the module docstring (formatting only).

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