Stardew valley: Add Marlon bedroom entrance rule (#3735)

* - Created a test for the "Mapping Cave Systems" book

* - Added missing rule to marlon's bedroom

* - Can kill any monster, not just green slime

* - Added a compound source structure, but I ended up deciding to not use it here. Still keeping it as it will probably be useful eventually

* - Use the compound source of the monster compoundium (ironic, I know)

* - Add required elevators

---------

Co-authored-by: NewSoupVi <57900059+NewSoupVi@users.noreply.github.com>

worlds/stardew_valley/data/game_item.py

@@ -59,6 +59,11 @@ class CustomRuleSource(ItemSource):
     create_rule: Callable[[Any], StardewRule]
 
 
+@dataclass(frozen=True, **kw_only)
+class CompoundSource(ItemSource):
+    sources: Tuple[ItemSource, ...] = ()
+
+
 class Tag(ItemSource):
     """Not a real source, just a way to add tags to an item. Will be removed from the item sources during unpacking."""
     tag: Tuple[ItemTag, ...]