chore: fix ruff lint failure

[voltjia]

Summary

• Removed the unused empty_strided import from tests/test_kv_caching_infinilm.py.
• Restored the Ruff workflow by making ruff check pass on master.

Motivation

The latest Ruff workflow on master failed before reaching the ruff format --check step because ruff check reported an unused import in tests/test_kv_caching_infinilm.py.

No related issue.

Type of Change

• feat — new feature / new operator / new platform
• fix — bug fix
• perf — performance improvement (no behavioral change)
• refactor — code restructuring without behavior change
• test — adding or fixing tests only
• docs — documentation only
• build / ci — build system or CI configuration
• chore — tooling, formatting, or other non-code changes
• Breaking change (requires a ! in the Conventional Commits prefix or a BREAKING CHANGE: footer)

Platforms Affected

• CPU (WITH_CPU)
• NVIDIA (WITH_NVIDIA)
• Iluvatar (WITH_ILUVATAR)
• MetaX (WITH_METAX)
• Cambricon (WITH_CAMBRICON)
• Moore (WITH_MOORE)
• Ascend (WITH_ASCEND)
• PyTorch C++ bindings (WITH_TORCH)
• Build system / CMake / CI
• Python bindings / user-facing API

Smoke Test Result

N/A - lint-only change. No runtime behavior changed.

Test Results on Supported Platforms

Platform	Affected	Build / Smoke Result	Full Result / Notes
NVIDIA	No	N/A - not affected	N/A - not affected
Iluvatar	No	N/A - not affected	N/A - not affected
MetaX	No	N/A - not affected	N/A - not affected
Cambricon	No	N/A - not affected	N/A - not affected
Moore	No	N/A - not affected	N/A - not affected
Ascend	No	N/A - not affected	N/A - not affected

Full `pytest` output (optional)

N/A - pytest was not run for this lint-only import cleanup.

Benchmark / Performance Impact

N/A - this removes an unused Python import only.

Notes for Reviewers

The failing GitHub Actions run was Ruff on master for commit 48e2f9841d93274ed8d7c75fade2725e6358d30c. The first chartboost/ruff-action@v1 step failed, and the format --check step was skipped.

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Checklist

Title, Branch, and Commits

• PR title follows Conventional Commits (e.g. feat(nvidia): …, fix(cuda/gemm): …).
• Branch name follows <type>/xxx-yyyy-zzzz where <type> matches the PR title's Conventional Commits type and words are joined with hyphens (see CONTRIBUTING.md §Branches).
• Each commit message follows Conventional Commits.
• Small PR is a single squashable commit; or, for a large PR, every commit is meaningful, well-formed, and independently reviewable (see CONTRIBUTING.md §Pull Requests).
• No stray merge commits from master — the branch is rebased cleanly on top of the current master.
• No fixup! / squash! / wip commits remain.

Scope and Design

• Changes are minimal — nothing unrelated to the stated motivation was added (CONTRIBUTING.md §Code/General).
• No dead code, commented-out blocks, debug prints, printf/std::cout/print(...) left behind, or TODO without an owner and issue link.
• No unrelated formatting churn that would obscure the diff.
• Public API changes (if any) are intentional, documented, and reflected in affected callers/tests. N/A - no public API changed.

General Code Hygiene (applies to all languages)

• The code is self-explanatory; comments were added only where the why is non-obvious (CONTRIBUTING.md §Code/General).
• Every modified or added file ends with a single trailing newline (CONTRIBUTING.md §Code/General).
• No trailing whitespace, tab/space mixing, or stray BOMs.
• Identifiers in comments and error messages are wrapped in backticks (e.g. the `seqlens_k` tensor) (CONTRIBUTING.md §Code/General). N/A - no comments or error messages changed.
• All comments and error messages are in English (CONTRIBUTING.md §Code/General). N/A - no comments or error messages changed.
• Comments and error messages are complete sentences — capitalized first letter, terminal punctuation — unless the language/framework convention says otherwise (CONTRIBUTING.md §Code/General; §Python). N/A - no comments or error messages changed.

C++ Specific (if C++ files changed)

N/A - no C++ files changed.

Python Specific (if Python files changed)

• Code is PEP 8 compliant; ruff check passes cleanly on CI (see .github/workflows/ruff.yml).
• ruff format --check passes cleanly — if not, run ruff format and commit the result.
• Comments are complete English sentences, starting with a capital letter and ending with punctuation; Markdown backticks are used for code references (CONTRIBUTING.md §Python). N/A - no comments changed.
• Framework-specific conventions (e.g. lowercase pytest.skip messages without terminal period) are honored where applicable. N/A - no messages changed.
• No blank line between the function signature and the body when there is no docstring or comment. N/A - no function bodies changed.
• A blank line is present before and after if, for, and similar control-flow statements. N/A - no control flow changed.
• A blank line appears before each return, except when it directly follows a control-flow statement. N/A - no returns changed.
• Docstrings (if any) follow PEP 257. N/A - no docstrings changed.
• Type hints are added / kept consistent with the surrounding code. N/A - no type hints changed.

Testing

• Smoke tests were run on every affected platform, and the results are recorded in the "Smoke Test Result" and platform table above. N/A - lint-only change with no affected runtime platform.
• Platforms that are not affected are marked N/A - not affected; any affected platform that could not be tested has an explicit reason and a reviewer or owner with access tagged.
• Full-suite or full-platform testing was run, or explicitly deferred, for high-risk changes and shared build/dispatch/wrapper-generation changes. N/A - not high risk.
• New functionality has matching tests under tests/ following tests/test_add.py / tests/test_gemm.py patterns. N/A - no new functionality.
• Tests use pytest.mark.parametrize correctly. N/A - no test parameterization changed.
• Where appropriate, pytest.mark.auto_act_and_assert is used and the test returns a Payload whose func and ref share the same calling convention. N/A - no test bodies changed.
• Default dtype / device parameterization is relied on, or overridden with an explicit pytest.mark.parametrize when necessary. N/A - no parameterization changed.
• Any new test that is flaky under parallelism is marked so, or documented to require pytest -n 1. N/A - no new tests.
• For bug fixes: a regression test has been added that fails on master and passes with this PR. N/A - lint-only cleanup; local ruff check covers the regression.

Build, CI, and Tooling

• The project builds cleanly from a fresh directory with pip install .[dev] on at least one affected platform. N/A - no build-affecting change.
• compile_commands.json still regenerates (CMake option CMAKE_EXPORT_COMPILE_COMMANDS=ON in pyproject.toml — required by the code-lint skill and clang-tidy -p). N/A - CMake configuration unchanged.
• New backends / devices have been added to auto-detection in CMakeLists.txt under if(AUTO_DETECT_DEVICES) and to if(AUTO_DETECT_BACKENDS) if applicable. N/A - no backend changes.
• Only one CUDA-like GPU backend is selectable at a time — the existing mutual-exclusion check in CMakeLists.txt is not broken. N/A - no backend changes.
• Both CI workflows (clang-format.yml, ruff.yml) are green locally (or expected to be green on CI). Local ruff check and ruff format --check passed; clang-format is N/A because no C++ files changed.
• No new runtime dependency was added without updating pyproject.toml's [project.optional-dependencies] (or justified in the PR description).

Documentation

• README.md, CONTRIBUTING.md, or inline docs updated when behavior, build flags, or developer workflow changed. N/A - no behavior or workflow changed.
• New operators, new dispatch helpers, or new public utilities are documented. N/A - none added.
• Any user-visible breaking change is called out explicitly under "Motivation" and in the commit/PR title with a ! or BREAKING CHANGE: footer. N/A - no breaking change.

Security and Safety

• No secrets, access tokens, internal URLs, customer data, or personal hardware identifiers have been committed.
• Third-party code is license-compatible and attributed. N/A - no third-party code added.
• No unsafe pointer arithmetic, uninitialized reads, or missing bounds checks were introduced. N/A - no native code changed.