Flag unused closure defined function / class definitions

[asottile]

I expect this to flag two errors:

def f():
    class IAmUnused: pass
    def i_am_unused(): pass

[adamchainz]

I mistakenly re-reported this on flake8 yesterday. The real world use case I saw was accidentally overly indented tests:

class MyTests(TestCase):
    def setUp(self):
        self.thing = Thing()
        
        def test_thing_1(self):
            self.assertEqual(self.thing.foo, "foo")

instead of:

class MyTests(TestCase):
    def setUp(self):
        self.thing = Thing()
        
    def test_thing_1(self):
        self.assertEqual(self.thing.foo, "foo")