Run doctests

[jarrodmillman]

Running

python -m pytest --cov=lazy_loader

works as expected; but running

python -m pytest --cov=lazy_loader --doctest-modules

yields

____________________ test_attach_same_module_and_attr_name _____________________

    def test_attach_same_module_and_attr_name():
        from lazy_loader.tests import fake_pkg
    
        # Grab attribute twice, to ensure that importing it does not
        # override function by module
>       assert isinstance(fake_pkg.some_func, types.FunctionType)
E       AssertionError: assert False
E        +  where False = isinstance(<module 'lazy_loader.tests.fake_pkg.some_func' from '/home/runner/work/lazy_loader/lazy_loader/lazy_loader/tests/fake_pkg/some_func.py'>, <class 'function'>)
E        +    where <module 'lazy_loader.tests.fake_pkg.some_func' from '/home/runner/work/lazy_loader/lazy_loader/lazy_loader/tests/fake_pkg/some_func.py'> = <module 'lazy_loader.tests.fake_pkg' from '/home/runner/work/lazy_loader/lazy_loader/lazy_loader/tests/fake_pkg/__init__.py'>.some_func
E        +    and   <class 'function'> = types.FunctionType

lazy_loader/tests/test_lazy_loader.py:104: AssertionError

[jarrodmillman]

See scientific-python/specs#151 and #29.