Stardew Valley: Move BaseTest out of __init__.py to comply with future conventions (#4991)

* move everything out of init; fix from imports and some typing errors

* why is there a change in multiserver

* fix some relative shits

worlds/stardew_valley/test/content/TestGingerIsland.py

@@ -1,5 +1,5 @@
 from . import SVContentPackTestBase
-from .. import SVTestBase
+from ..bases import SVTestBase
 from ... import options
 from ...content import content_packs
 from ...data.artisan import MachineSource