I'm hesitating to merge this for same reason as here: #2163 (comment)

With this update, users need to update their PHPDocs with numeric-string...

If it can help with deciding, bcadd(and others) is documented as taking numeric-strings in Psalm for almost 3 years now: vimeo/psalm#3189

As far as I know, no one complained about that. Though I admit it may be biased because users likely to come and create an issue are users that generally will want more strict checks,

I'm hesitating to merge this for same reason as here: #2163 (comment)

With this update, users need to update their PHPDocs with numeric-string...

but that's a good thing, right? I mean: if they accept user string - the method that returns that string will be just string - so phpstan will force them to take that string through is_numeric check, otherwise they will get an exception in runtime - which is basically what static analysers are trying to prevent.

Commited as 3fb919a