fix(tf): handle multiframe DeepSpin extension

[njzjz-bot]

Closes #5660.

Summary

• build TensorFlow DeepSpin physical and virtual coordinate buffers for every input frame in both direct and external-neighbor-list paths
• separate extended coordinate frame strides from original-atom aparam strides during NULL-atom selection
• copy physical force, magnetic force, atomic energy, and atomic virial outputs with explicit source/destination frame offsets
• derive the atomic-energy source width from the TensorFlow tensor, since spin models emit energies only for physical atoms while C++ preserves extended virtual slots
• add distinct two-frame direct and InputNlist atomic regressions for both double and float

Why existing tests missed this

All TensorFlow DeepSpin C++ tests used scalar-energy, single-frame calls. The extension helpers therefore only needed frame-zero buffers, and frame-zero copyback filled every asserted output. No test exercised the documented vector-energy overload with nframes > 1, so undersized extension buffers, incorrect inferred frame counts, and missing output frame offsets remained invisible.

The new tests perturb both coordinates and spins in frame 2, evaluate each frame separately, and compare every batched slice against its one-frame reference. They also assert the frame references differ, preventing duplicated-frame behavior from passing.

Validation

• ruff format .
• ruff check .
• clang-format --dry-run --Werror on all changed C++ files
• built deepmd_op, deepmd_backend_tf, and runUnitTests_cc
• all 16 TestInferDeepSpin and TestInferDeepSpinNopbc typed tests passed
• focused four-case two-frame matrix passed: direct/InputNlist × double/float

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

[codecov]

Codecov Report

❌ Patch coverage is 2.12766% with 92 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.33%. Comparing base (6c3b985) to head (1250729).

Files with missing lines	Patch %	Lines
source/api_cc/tests/test_deeppot_tf_spin.cc	0.00%	92 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (6c3b985) and HEAD (1250729). Click for more details.

HEAD has 42 uploads less than BASE

Flag	BASE (6c3b985)	HEAD (1250729)
	56	14

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5851      +/-   ##
==========================================
- Coverage   78.58%   70.33%   -8.25%     
==========================================
  Files        1050     1024      -26     
  Lines      120637   114250    -6387     
  Branches     4356     3535     -821     
==========================================
- Hits        94801    80357   -14444     
- Misses      24278    33088    +8810     
+ Partials     1558      805     -753     

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[njzjz]

Possible reviewers based on changed lines, exact file history, and exact-file review history:

• @wanghan-iapcm — 4 commits on changed files; 20 reviews on exact changed files (source/api_cc/src/DeepSpinTF.cc, source/api_cc/src/common.cc).
• @OutisLi — 12 reviews on exact changed files (source/api_cc/src/common.cc).

No review request was made automatically.

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