Adds 3.14 Free Threading support

[kingbuzzman]

Removed Django 5.1 classifier and added 3.14 Free Threading support.
Removed psycopg[binary] in favor of psycopg (the full python implementation) to avoid issues with 3.14t
Removed support for dj5.1

[bluetech]

Thanks @kingbuzzman.

Regarding 3.14t, I think pytest-dev/pluggy#621 (review) is the current approach in pytest. I think until pytest itself adds 3.14t we should hold on it in pytest-django.

That said, pytest-django is pure python, 3.14t should work perfectly fine, as long as not trying to run pytest/pytest-django in multiple threads, as they are not thread safe.

Dropping Django 5.1 is good though.

[kingbuzzman]

Regarding 3.14t, I think pytest-dev/pluggy#621 (review) is the current approach in pytest.

@bluetech I was going off this that @cclauss requested