mypy

https://github.com/readthedocs/recommonmark#recommonmark

We should switch to myst: https://github.com/executablebooks/MyST-Parser

With the recent bug-fix in #1463, I noticed a lack of tests directly testing UnionDefinition.get_type_resolver and the function that it returns. We should add these.

https://github.com/readthedocs/recommonmark#recommonmark

We should switch to myst: https://github.com/executablebooks/MyST-Parser

When we define a class like this:

def func():
    ...

class MyClass:
    my_func = lambda self, arg: arg

# or
class MyAnotherClass:
    my_func = func

The coverage plugin will consider the my_func as coveraged without any tests.
This behavior is expected because for it the my_func is an attribute!

I think it will be great use the normal signature, this will en