fix: PHP 8.4 Take 3

[phpfui]

Fixes

While #839 fixed the non-generated code, the generated code still has the problem of typed parameters with a null default value. This produces depreciation messages in PHP 8.4

This PR adds the PHP CS Fixer and configuration so that the generated code can be automatically updated to be PHP 8.4 compatible.

I was unable to find the place where the code is generated by https://openapi-generator.tech, so this PR will need additional work to automatically update the code after generation.

To fix the generated code, just enter this command:

composer run-script php84-fix

The resulting code should then be checked into the repo. This should be able to be automated and run immediately after code generation.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified