docs(guidelines): Add instructions to skip code formatting

[lucasssvaz]

Description of Change

This pull request updates the documentation to clarify how to selectively disable and enable automatic code formatting in C/C++ files using special comments. This helps contributors maintain specific formatting where needed.

Documentation improvements:

• Added instructions and an example for using // clang-format off and // clang-format on comments to control code formatting in specific code sections in the coding guidelines (docs/en/guides/coding_guidelines.rst).

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[Copilot]

Pull request overview

This PR updates the Arduino ESP32 coding guidelines documentation to describe how contributors can selectively disable automatic clang-format formatting in C/C++ source sections when a specific layout must be preserved.

Changes:

• Documented the use of // clang-format off and // clang-format on markers to disable/re-enable formatting.
• Added a short C example demonstrating the formatting suppression behavior.

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