feat(entity): add client-to-server entity creation and destruction requests

Extend the network protocol with `C2SEntityCreateRequest` and `C2SEntityDestoryRequest` packets. Refactor entity managers to split public client-facing create/destroy methods that send requests over the network, from internal handlers that process received packets. Add utility functions for converting protobuf Vec3 to glm::vec3.

src/gameplay/server_entity_manager.cpp

@@ -17,8 +17,9 @@ void ServerEntityManager::init() {
     m_factories.try_emplace("cubed:pig", [this]() {
         BaseServerCreature c;
         c.hitbox = HitboxManager::instance().get_hitbox_id("cubed:pig");
-        return add_entity(Entity{m_next}, EntityInfo{"cubed:pig", ""},
-                          std::move(c), PigTag{});
+        return create_entity_in_factory(Entity{m_next},
+                                        EntityInfo{"cubed:pig", ""},
+                                        std::move(c), PigTag{});
     });
 }
 void ServerEntityManager::update() { handle_task(); }