Mark the public class constants as @internal

[oliverklee]

Those class constants are not intended to be accessed from outside this package.

[sabberworm]

Do they need to be public at all?

[oliverklee]

Do they need to be public at all?

Some of them, yes, as they are either part of an interface (where only public consts are possible), or because they are accessed from another class.

[JakeQZ]

Do they need to be public at all?

Setting the visibility of class constants (e.g. with private const) has only been possible since PHP 7.1. So it's only now possible to clear this up since dropping the older PHP versions.