Add callable typing + type testing

[WyriHaximus]

To get this package fully type safe PHPStan supports type testing to ensure every type is working as intended. How to do this is described in https://blog.wyrihaximus.net/2024/06/updating-php-packages-to-reactphp-promise-v3--and-test-your-types-with-phpstan/ .

For more reference material I'm doing the same thing in reactphp-parallel/event-loop#51

[ericsizemore]

Hmm. I seem to recall running into some issues in trying to template the callables. I may have to take another look myself, since it's been several months. I haven't dove too deep into PHPStan 2 so I'm not sure what, if any, improvements they've made to typing Closures/callables.

[ericsizemore]

Hmm. I seem to recall running into some issues in trying to template the callables. I may have to take another look myself, since it's been several months. I haven't dove too deep into PHPStan 2 so I'm not sure what, if any, improvements they've made to typing Closures/callables.

Unfortunately I've not been able to look any further into this myself. I'm having to focus quite a bit on my health these days, so beyond some automated stuff on my own repos I've not been able to do much.

Hopefully I'll be able to at some point, but if anyone else wants to help take this on please do. :)