Support for readonly classes

[stof]

https://wiki.php.net/rfc/readonly_classes

[kschatzle]

@stof anyone working on the PHP8.2? Don't want to duplicate work, but I can pick these up.

[kschatzle]

Was playing around with this idea. Essentially make the underlying "testing" class be capable of being readonly. Can't be sure if this is a good idea, just playing with it.

https://gist.github.com/kschatzle/5394a3abc427659d21ef6f854e01c0f6

[stof]

@kschatzle not that I'm aware off.

[stof]

Note that the initial compat with PHP 8.2 might be to have a clear error message saying that doubling a readonly class is not supported yet, in case supporting this case require more time.

[kschatzle]

Ok, yeah, I saw some isFinal checks in various places. I could see a similar isReadOnly() working similar.

[ciaranmcnulty]

Yeah I've not seen any activity on it so go ahead if you have the time

[kschatzle]

Initial support as requested. #564