test: add pytest.ini for easier test running

- Set testpaths = tests
- Set pythonpath = . (no need for PYTHONPATH=. prefix)
- Set asyncio_default_fixture_loop_scope = function

pytest.ini

@@ -0,0 +1,4 @@
+[pytest]
+testpaths = tests
+pythonpath = .
+asyncio_default_fixture_loop_scope = function