Exposing a fixture for deferred factory evaluation

It'd be nice to be able to expose a fixture (maybe the factory fixture?) that can be invoked in the test invocation.

Here's a few use cases:

• creating the object when using a decorator, e.g. factory.django.mute_signals(signals.post_save)
• create the object imperatively in the test body, for example if you use @pytest.mark.django_db(transactional=True), and you need to create your object within a django.db.transaction.atomic() context manager.

class Book:
    name: str

class BookFactory(Factory):
    name = "foo"


@pytest.mark.parametrize("book__name", ["bar"])
def test_book_initialise_later(book_factory):
    book = book_factory()
    assert book.name == bar

Start by tracing the pytest fixture integration and the existing factory fixture behavior, then use the book_factory example and its pytest.mark.parametrize case as the expected entry point. The work is done when a factory can be invoked inside the test body and supports deferred creation for decorator and transactional django.db.transaction.atomic() use cases.