Test suite: test_subtract_overscan calls numpy-only .copy() on array-API arrays

[mwcraig]

Under CCDPROC_ARRAY_LIBRARY=array-api-strict, all 6 parametrized variants of test_subtract_overscan fail with the same error:

ccdproc/tests/test_ccdproc.py:174: in test_subtract_overscan
    science_data = ccd_data.data[science_region].copy()
E   AttributeError: 'Array' object has no attribute 'copy'

Offending code — ccdproc/tests/test_ccdproc.py:174-175 (branch array-api-strict-triage-tooling):

science_data = ccd_data.data[science_region].copy()
overscan_data = 0 * ccd_data.data[oscan_region].copy() + oscan

Root cause: the Array API standard does not include a .copy() method on arrays; the portable spelling is xp.asarray(..., copy=True).

This is test-only. The library code is not implicated: core.py's subtract_overscan only calls .copy() on a CCDData object, which is unaffected. The fix belongs in the test suite:

science_data = xp.asarray(ccd_data.data[science_region], copy=True)
overscan_data = 0 * xp.asarray(ccd_data.data[oscan_region], copy=True) + oscan

(the xp namespace is already available in the test function).

Part of the array-API triage in #941; found with the array-api-strict tooling from #937/#939. Verified at branch tip d329ac5 (2026-08-01). Related test-suite cleanup of the same kind: raw np.zeros_like calls, tracked separately.

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