set phpstan to level max and fix issues

[oallain]

Hello,

I do:

• Set PHPStan to level max (ie 8) https://phpstan.org/user-guide/rule-levels.
• Fix issues throws by PHPStan
• Add PHPStan to Travis

It improve DX 🚀

[oallain]

Hello @dragonmantank,

I use this librairie and i love it, so i propose my first PR :)
I hope this will help you, and i'm available for more updates.

Regards

[dragonmantank]

Thanks! Could you possibly rebase on the newest master branch? After your PR was created there was an update to support PHP 8, which generated a few conflicts

[oallain]

Hello @dragonmantank ,

I've juste rebase on master 🎉

I'll propose an other PR to add PHPStan chek with Github Actions.

[oallain]

Hello @dragonmantank

Do you have any time to review this PR?

Thanks

[dragonmantank]

Manually merged this, just had a few cleanup issues due to other fixes. Thanks!

[oallain]

Good job @dragonmantank 💪
Thanks for that !