Respect array namespaces when Bottleneck is installed

[nomad3]

Summary

• use Bottleneck's NaN-aware reductions only for NumPy or an unspecified array namespace
• use the selected backend's native reductions for non-NumPy arrays
• resolve average and sum uncertainty/reduction defaults at call time, after the data namespace is known
• exercise both NumPy+Bottleneck and Dask+Bottleneck in CI

Fixes #904

Validation

• failing-first on untouched main, Dask+Bottleneck test_combiner.py: 35 failed, 39 passed
• focused namespace regressions: 6 passed with Dask+Bottleneck and 6 passed with NumPy+Bottleneck
• full Combiner module: 80 passed with Dask+Bottleneck and 80 passed with NumPy+Bottleneck
• full NumPy suite: 342 passed, 29 skipped
• full Dask suite: 337 passed, 34 skipped
• full JAX x64 suite: 335 passed, 29 skipped, 7 established xfails
• black --check ccdproc/combiner.py ccdproc/tests/test_combiner.py
• ruff check ccdproc/combiner.py ccdproc/tests/test_combiner.py
• workflow YAML parse and git diff --check

AI assistance disclosure

I used OpenAI Codex to assist with repository inspection, test design, implementation, and review. I reviewed the resulting changes and take responsibility for their correctness and maintenance.

Checklist

• For new contributors: Did you add yourself to the AUTHORS.rst file? (The entry is already in draft PR Exclude masked weights from average combinations #952 and is not duplicated here.)
• For documentation changes: Does your commit message include a [skip ci]? (Not applicable.)
• Did you add an entry to the CHANGES.rst file?
• Did you add a regression test?
• Does the commit message include a Fixes #issue_number?
• Does this PR add, rename, move or remove any existing functions or parameters? (No; existing defaults are resolved at call time.)

[codecov]

Codecov Report

❌ Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.82%. Comparing base (3ea1af9) to head (b78287c).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
ccdproc/combiner.py	76.47%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #959      +/-   ##
==========================================
- Coverage   96.70%   95.82%   -0.88%     
==========================================
  Files           8        8              
  Lines        1576     1628      +52     
==========================================
+ Hits         1524     1560      +36     
- Misses         52       68      +16     

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[mwcraig]

thanks, @nomad3!

Thanks for fixing the old ubuntu-py312-bottleneck job that never actually installed bottleneck (its tox env lacked the bottleneck factor, and alldeps doesn't include it) — which is why CI never caught #904. The env rename here makes that job real
for the first time.