fix(gameplay): use inline const for static EMPTY members

Use inline const for static EMPTY members to avoid ODR and linker issues.
Add missing block_manager.hpp includes in gameplay sources.

include/Cubed/gameplay/block_manager.hpp

@@ -34,7 +34,7 @@ private:
     using IDMap = tbb::concurrent_hash_map<std::string, BlockType>;
     using CrossPlaneMap = tbb::concurrent_hash_map<BlockType, BlockType>;
 
-    static const BlockData EMPTY;
+    static inline const BlockData EMPTY;
 
     static inline BlockMap m_datas;
     static inline IDMap m_id_map;

include/Cubed/gameplay/item_manager.hpp

@@ -34,6 +34,6 @@ private:
     IDMap m_id_map;
     BlockToIDMap m_block_to_id_map;
 
-    static constexpr ItemData EMPTY;
+    static inline const ItemData EMPTY;
 };
 } // namespace Cubed

src/gameplay/chunk_generator.cpp

@@ -1,5 +1,6 @@
 #include "Cubed/gameplay/chunk_generator.hpp"
 
+#include "Cubed/gameplay/block_manager.hpp"
 #include "Cubed/gameplay/builders/desert_builder.hpp"
 #include "Cubed/gameplay/builders/forest_builder.hpp"
 #include "Cubed/gameplay/builders/mountain_builder.hpp"

src/gameplay/client_chunk.cpp

@@ -1,5 +1,6 @@
 #include "Cubed/gameplay/client_chunk.hpp"
 
+#include "Cubed/gameplay/block_manager.hpp"
 namespace Cubed {
 using OptionalBlockVectorArray =
     std::array<std::optional<std::vector<BlockType>>, 4>;

src/gameplay/client_player_manager.cpp

@@ -1,9 +1,9 @@
 #include "Cubed/gameplay/client_player_manager.hpp"
 
+#include "Cubed/gameplay/block_manager.hpp"
 #include "Cubed/gameplay/client_world.hpp"
 #include "Cubed/gameplay/hitbox_manager.hpp"
 #include "Cubed/tools/math_tools.hpp"
-
 using namespace google::protobuf;
 
 namespace Cubed {

src/gameplay/client_world.cpp

@@ -1,6 +1,7 @@
 #include "Cubed/gameplay/client_world.hpp"
 
 #include "Cubed/config.hpp"
+#include "Cubed/gameplay/block_manager.hpp"
 #include "Cubed/gameplay/chunk_generator.hpp"
 #include "Cubed/gameplay/game_time.hpp"
 #include "Cubed/gameplay/packet.hpp"

src/gameplay/item_manager.cpp

@@ -15,6 +15,7 @@ ItemManager::ItemManager() {}
 
 ItemManager& ItemManager::instance() {
     static ItemManager inst;
+
     return inst;
 }
 

src/gameplay/server_world.cpp

@@ -1,5 +1,6 @@
 #include "Cubed/gameplay/server_world.hpp"
 
+#include "Cubed/gameplay/block_manager.hpp"
 #include "Cubed/gameplay/packet.hpp"
 #include "Cubed/gameplay/session.hpp"
 #include "Cubed/tools/cubed_assert.hpp"