[chore] exclude dev files from Composer dist archive

[alissn]

Summary

This PR updates .gitattributes to exclude development, CI, test, and documentation files from Composer dist archives.

Description

When the Package is installed via Composer, the downloaded package currently includes files that are not needed at runtime, such as:

• GitHub workflows
• tests
• PHPUnit / PHPStan / PHPCS / Rector configs
• Docker and Make files
• contribution templates

This increases the package download size and adds unnecessary files to the vendor/ directory.

Runtime files such as src/, config/, resources/, composer.json, LICENSE.md, and README.md are intentionally kept.

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