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/mods/TestSVE.py

@@ -1,5 +1,5 @@
 from .. import SVContentPackTestBase
-from ... import SVTestBase
+from ...bases import SVTestBase
 from .... import options
 from ....content import content_packs
 from ....mods.mod_data import ModNames