Core: typing and cleaning, mostly in Fill.py (#4459)

* Core: typing and cleaning, mostly in `Fill.py`

* fix typing of things we get out of plando blocks

* clean getting multiworld from kwargs
add a list type
clean indentation

* fix issues with merge conflict resolution

* some things found after merge

BaseClasses.py

@@ -514,7 +514,7 @@ class MultiWorld():
         state.can_reach(Region) in the Entrance's traversal condition, as opposed to pure transition logic."""
         self.indirect_connections.setdefault(region, set()).add(entrance)
 
-    def get_locations(self, player: Optional[int] = None) -> Iterable[Location]:
+    def get_locations(self, player: int | None = None) -> Collection[Location]:
         if player is not None:
             return self.regions.location_cache[player].values()
         return Utils.RepeatableChain(tuple(self.regions.location_cache[player].values()