fix(lammps): emit valid spin atom style sections

[njzjz-bot]

Fixes #885.

Mark spin-vector data as Atoms # spin, support automatic spin-style parsing, and validate the generated file with LAMMPS.

Tests: cd tests && python -m unittest test_lammps_spin (LAMMPS integration skips when the executable/package is unavailable).

Why existing tests missed it: The previous test only inspected text; it emitted nine-column spin rows under an atomic-style header that LAMMPS rejects.

Coding agent: Codex
Codex version: codex-cli 0.144.4
Model: gpt-5.6-sol
Reasoning effort: xhigh

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📥 Commits

Reviewing files that changed from the base of the PR and between 0416b54 and c7cdaac.

📒 Files selected for processing (3)

• dpdata/formats/lammps/lmp.py
• dpdata/plugins/lammps.py
• tests/test_lammps_spin.py

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[codspeed-hq]

Merging this PR will not alter performance

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✅ 2 untouched benchmarks

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_{Comparing njzjz-bot:fix/issue-885 (c7cdaac) with master (0416b54)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.87%. Comparing base (0416b54) to head (c7cdaac).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1032   +/-   ##
=======================================
  Coverage   86.87%   86.87%           
=======================================
  Files          89       89           
  Lines        8266     8269    +3     
=======================================
+ Hits         7181     7184    +3     
  Misses       1085     1085           

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[wanghan-iapcm]

The #885 fix looks correct and matches LAMMPS's atom_style spin layout (id type x y z spx spy spz sp), and the assertIn("Atoms # spin", ...) test genuinely fails on pre-fix code (which emitted # atomic). One coordination note with the open PR #1020, which modifies the same get_spins guard -- see inline.

[wanghan-iapcm]

Heads-up: the still-open PR #1020 (fix/issue-995) adds this exact guard (if atom_style not in {"atomic", "spin"}: return None) -- only the comment placement differs. They branch from a shared merge-base, so git merge-tree shows one add/add conflict right here; whichever of #1020 / #1032 merges second will hit it (cosmetic -- identical logic).

This PR is the natural completion of #1020: #1020's whitelist references "spin" but never registered it in ATOM_STYLE_COLUMNS, so that arm was dead code -- the "spin" entry added here (line 25) makes it live, and emitting Atoms # spin fixes the # spin-labeled-file regression #1020 introduced. Suggest sequencing them: merge one, then rebase the other and drop the duplicate guard hunk (keep #1020's detect_atom_style neutral-charge fix + tests, keep #1032's dict entry + writer).

[njzjz]

Agreed on the sequencing. No code change is appropriate until either #1020 or #1032 merges. After the first PR lands, the other branch should be rebased and the duplicate get_spins guard hunk dropped while preserving #1020's detection fixes and #1032's real spin-style definition and writer support. I am leaving this thread unresolved until that coordination step can be completed.

Coding agent: Codex
Codex version: codex-cli 0.144.6
Model: gpt-5.6-sol
Reasoning effort: xhigh