refactor: hide implementation of loading steps inside file

src/ZoneLoading/Loading/Steps/StepAddProcessor.cpp

@@ -2,15 +2,33 @@
 
 #include <cassert>
 
-StepAddProcessor::StepAddProcessor(std::unique_ptr<StreamProcessor> streamProcessor)
-    : m_stream_processor(std::move(streamProcessor))
+namespace
 {
-}
+    class StepAddProcessor final : public ILoadingStep
+    {
+    public:
+        explicit StepAddProcessor(std::unique_ptr<StreamProcessor> streamProcessor)
+            : m_stream_processor(std::move(streamProcessor))
+        {
+        }
 
-void StepAddProcessor::PerformStep(ZoneLoader& zoneLoader, ILoadingStream& stream)
+        void PerformStep(ZoneLoader& zoneLoader, ILoadingStream& stream) override
+        {
+            assert(m_stream_processor != nullptr);
+
+            zoneLoader.AddStreamProcessor(std::move(m_stream_processor));
+            m_stream_processor = nullptr;
+        }
+
+    private:
+        std::unique_ptr<StreamProcessor> m_stream_processor;
+    };
+} // namespace
+
+namespace step
 {
-    assert(m_stream_processor != nullptr);
-
-    zoneLoader.AddStreamProcessor(std::move(m_stream_processor));
-    m_stream_processor = nullptr;
-}
+    std::unique_ptr<ILoadingStep> CreateStepAddProcessor(std::unique_ptr<StreamProcessor> streamProcessor)
+    {
+        return std::make_unique<StepAddProcessor>(std::move(streamProcessor));
+    }
+} // namespace step