workflows: Add clang format check workflow.

[soburi]

Cherry-pick the commit adding .clang-format from https://github.com/arduino/ArduinoCore-zephyr.

[Copilot]

Pull request overview

This PR adds automated clang-format checking to the CI pipeline by cherry-picking configuration from the ArduinoCore-zephyr repository. The workflow will run on code changes to C/C++ files and enforce consistent code formatting across the project.

• Adds GitHub Actions workflow for automated clang-format validation
• Introduces comprehensive clang-format configuration based on LLVM style with Zephyr-specific customizations
• Configures format checking for specific project directories (cores/arduino, loader, libraries) with selective exclusions

Reviewed changes

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

File	Description
.github/workflows/format_check.yml	New workflow that triggers format checks on C/C++ file changes using clang-format v19 across multiple project directories
.clang-format	Configuration file defining LLVM-based formatting rules with Zephyr macros, 100-column limit, and project-specific style preferences

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[Copilot]

The matrix configuration has duplicate 'exclude' keys. In YAML, when the same key appears multiple times at the same level, only the last value is retained. This means only 'ea_malloc' will be excluded, and the 'loader/llext_exports.c$' and 'examples' exclusions will be ignored. These should be combined into a single exclude pattern using regex alternation, or the matrix structure should be redesigned to support multiple exclusions per path.

Suggested change

	exclude: 'examples'
	exclude: 'extras'
	exclude: 'ea_malloc'
	exclude: 'examples|extras|ea_malloc'

[Copilot]

There is trailing whitespace after 'Log level' on this line. This should be removed to maintain consistent code formatting.

Suggested change

	description: 'Log level'
	description: 'Log level'