Physics Interpolation - Flush transforms after physics tick

Leftover transforms from the physics tick were being flushed during idle, which was causing problems for physics interpolation.

This PR flushes the transforms at the end of the physics tick when physics interpolation is active.

core/os/main_loop.h

@@ -68,6 +68,7 @@ public:
 
 	virtual void init();
 	virtual bool iteration(float p_time);
+	virtual void iteration_end() {}
 	virtual bool idle(float p_time);
 	virtual void finish();
 

main/main.cpp

@@ -2257,6 +2257,8 @@ bool Main::iteration() {
 
 		message_queue->flush();
 
+		OS::get_singleton()->get_main_loop()->iteration_end();
+
 		physics_process_ticks = MAX(physics_process_ticks, OS::get_singleton()->get_ticks_usec() - physics_begin); // keep the largest one for reference
 		physics_process_max = MAX(OS::get_singleton()->get_ticks_usec() - physics_begin, physics_process_max);
 		Engine::get_singleton()->_physics_frames++;

scene/main/scene_tree.cpp

@@ -525,6 +525,14 @@ void SceneTree::client_physics_interpolation_remove_spatial(SelfList<Spatial> *p
 	_client_physics_interpolation._spatials_list.remove(p_elem);
 }
 
+void SceneTree::iteration_end() {
+	// When physics interpolation is active, we want all pending transforms
+	// to be flushed to the VisualServer before finishing a physics tick.
+	if (_physics_interpolation_enabled) {
+		flush_transform_notifications();
+	}
+}
+
 bool SceneTree::iteration(float p_time) {
 	root_lock++;
 

scene/main/scene_tree.h

@@ -306,6 +306,7 @@ public:
 	virtual void init();
 
 	virtual bool iteration(float p_time);
+	virtual void iteration_end();
 	virtual bool idle(float p_time);
 
 	virtual void finish();