refactor(client_player): return ChunkPosSet by value in non-const getter

Copy the internal set under the mutex lock to avoid exposing a mutable reference that could be used unsafely after the lock is released. This fixes a potential data race when the caller holds the returned reference beyond the critical section. Also update the caller in `client_world` to remove the now-unnecessary `std::move`.

include/Cubed/gameplay/client_player.hpp

@@ -25,7 +25,7 @@ public:
 
     void update_chunk_set(const ChunkPosSet& set);
     const ChunkPosSet& get_chunk_pos_set() const;
-    ChunkPosSet& get_chunk_pos_set();
+    ChunkPosSet get_chunk_pos_set();
 
     static AABB get_aabb(const glm::vec3& pos);
     const glm::vec3& get_front() const;

src/gameplay/client_player.cpp

@@ -561,7 +561,7 @@ const ClientPlayer::ChunkPosSet& ClientPlayer::get_chunk_pos_set() const {
     return m_player_chunk_pos_set;
 }
 
-ClientPlayer::ChunkPosSet& ClientPlayer::get_chunk_pos_set() {
+ClientPlayer::ChunkPosSet ClientPlayer::get_chunk_pos_set() {
     std::lock_guard lock(m_chunk_pos_mutex);
     return m_player_chunk_pos_set;
 }

src/gameplay/client_world.cpp

@@ -590,7 +590,7 @@ void ClientWorld::request_chunk() {
         }
     }
 
-    ChunkPosSet old = std::move(m_player.get_chunk_pos_set());
+    ChunkPosSet old = m_player.get_chunk_pos_set();
     m_player.update_chunk_set(required_chunks);
 
     ChunkPosVector need_send_pos;