Add static analysis

[matthewtrask]

so this way people can run these tools locally, before they hit CI.

[Nyholm]

Im not a big fan of this. I believe PHPstan and Psalm are tools, just like PHPStorm. All three will help you two write better code and none is integrated like PHPUnit.

I am the kind of programmer that always make 2-3 commits per pull request to fix the issues after CI is run. But I also know that other people would like to fix CS issues before they push.

So I am more like ¯\(ツ)/¯. Merge it if you like.
But let's remove it if/when it causes dependency issues.

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FYI, I've installed these tool globally on my machine.

[matthewtrask]

@Nyholm thats all fair! I tend to stick to by project installs for some reason. I will merge for the moment, but like you said if the dependencies get messy we can definitely remove it.