bump to php 8.1, add typehints, etc.

[tacman]

Since PHP 5 is long-dead, PHP 7 still kinda long dead, and php 8.0 recently EOL, what do you think about a version 2 that simply updates the minimum requirements to php 8.1 and then updates the code to reflect all the new features, like type-hinting?

It's mostly for a better Developer Experience, with typehints and property injection.

I can do it (probably using Rector, which makes these kind of things easy), if you'll accept a PR and release a new version.