Add Toonable interface and ToonFormat trait

[WendellAdriel]

Summary

• Add Toonable interface contract for objects that can be converted to TOON format
• Add ToonFormat trait providing toToon() method implementation
• Add comprehensive test coverage for default and custom encoding options
• Update .gitignore to exclude .phpunit.cache/ and .idea/
• Configure Pest to run tests in parallel mode

Test plan

• Test default TOON encoding with UserDTO
• Test custom encoding options (custom delimiter)
• Verify trait correctly invokes the toon encoder via Laravel service container

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