Update for fastify@5.0.0

[Bram-dc]

• Added support for fastify@5.0.0
• Added refs
• Changed ResponseValidationError
• Throw correct error when input is invalid
• Updated dependencies
• Switched to eslint flat config

This is for my own release on NPM, but it might be a good idea to not have duplicate packages and incoorporate the changes into this repo.

[LucasCavalheri]

great job!