[refactor] Sync with master

This was initially a merge commit that got ironed out by rebase cleanup.
Notable changes are:
- Copying EntityRef instead of referencing it
- Some changes to includes

src/Entities.hpp

@@ -1,19 +1,16 @@
 #pragma once
 
 #include "core/Core.hpp"
-#include "Chunking.hpp"
 
 #include "EntityRef.hpp"
 #include "Buffs.hpp"
+#include "Chunking.hpp"
+#include "Groups.hpp"
 
 #include <set>
 #include <map>
 #include <functional>
 
-/* forward declaration(s) */
-class Chunk;
-struct Group;
-
 enum class AIState {
     INACTIVE,
     ROAMING,