Support PHP 8.4

[tacman]

I've made some changes to the code to support PHP 8.4, but I'm stuck on the testing. phpstan is locked to 2.1.0, which depends on the phpstan-rules, which is locked to a version that doesn't support PHP 8.4, only up to PHP 8.3.

The latest versions of all these packages will work with 8.4, but I'm not familiar with how to update them.

In particular, simply allow later versions threw new error messages.

DigitalOceanPHPClient/vendor-bin/phpstan$ cat composer.json

{
    "require": {
        "php": "^8.1",
        "phpstan/phpstan": "1.10.47 || ^2.0",
        "phpstan/phpstan-deprecation-rules": "1.1.4",
        "phpstan/phpstan-strict-rules": "1.5.2",
        "thecodingmachine/phpstan-strict-rules": "1.0.0",
        "ergebnis/phpstan-rules": "^2.1.0"
    },
    "config": {
        "preferred-install": "dist"
    }
}

I'm not sure how to proceed from here. The code itself I think I can fix (using rector) to support 8.4, but I can't get past the tests.

https://github.com/tacman/DigitalOceanPHPClient/actions/runs/12431381922/job/34708692209

Any suggestions?