Add cpp-linter action

[Mousius]

This uses the same .clang-format as numpy for consistency.

[Mousius]

@seiko2plus do you think this is good enough, or do you think we should set up spin to match the main repo?

[Copilot]

Pull Request Overview

Adds a C++ linting step to CI and ensures consistent formatting with NumPy’s .clang-format.

• Introduces a GitHub Actions workflow (cpp-linter.yml) that runs a C++ linter on changes under npsr/.
• Adds a .clang-format file mirroring NumPy’s style for uniform code formatting.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.github/workflows/cpp-linter.yml	New CI workflow to run a C++ linter via the cpp-linter-action.
.clang-format	Clang-Format configuration based on NumPy’s style guidelines.

Comments suppressed due to low confidence (1)

.clang-format:28

• The regex for matching angled includes uses a closing quote (") instead of a closing angle bracket (>). It should be ^<[[:alnum:]_.]+> to properly match <header> patterns.

  - Regex:           '^<[[:alnum:]_.]+'"

[Copilot]

GitHub Actions outputs are treated as strings; comparing checks-failed to an unquoted number may always evaluate to true. Use != '0' or compare as a string to correctly detect failures.

Suggested change

	if: steps.linter.outputs.checks-failed != 0
	if: steps.linter.outputs.checks-failed != '0'

[seiko2plus]

I followed google style without any modifications in #1 to match with Highway, but its okay to reformat it.. I just followed Highway because I thought that's maybe its better to target Highway community in case of there's need to move/share any code..

[seiko2plus]

do you think this is good enough, or do you think we should set up spin to match the main repo?

For now its fine to me.. I just add it spin within #1, with support of spin commands (test, generate, python, ipython)

[seiko2plus]

@Mousius, Thank you!