Improve (beginner) UX around self vs. fixtures

Something I see sometimes in my pytest company trainings is people accidentally doing:

def test_something(self):
    ...

because they're using to writing things in classes (e.g. from Java?). That results in a

E       fixture 'self' not found
>       available fixtures: [quite a long list here]
>       use 'pytest --fixtures [testpath]' for help on them.

which is not exactly useful if you don't know yet what a fixture is. IMHO, we should detect the self name here, and output an additional hint ("hint: Remove self as this is not a method?" or somesuch).

Similarly, when people start moving tests from functions to classes, they forget to add self, which can be very confusing in combination with fixtures:

class TestSomething:

    def test_x(monkeypatch):
        monkeypatch.setenv("DEBUG", "true")

results in:

    def test_x(monkeypatch):
>       monkeypatch.setenv("DEBUG", "true")
E       AttributeError: 'TestSomething' object has no attribute 'setenv'

which is still somewhat clear, but depending on what you do with a fixture (e.g. passing data to a function under test), it can be quite confusing if you've never seen this kind of message before.

Maybe a bit more tricky here, but it would be nice if pytest could detect that we're in a test method, the first argument is not self, and the first argument is a valid fixture name. If all of those are true, that seems to be worth warning about as well.

No files or tests are named in the issue. Start by tracing pytest's fixture lookup and test-method argument handling, then add coverage for both shown examples; done means actionable hints appear for mistaken self usage without changing valid fixture behavior.