Properly gate imports in bevy_scene (#18482)

# Objective

- Some imports are only used with certain features.

## Solution

- Gate them!

## Testing

- CI

crates/bevy_scene/src/dynamic_scene.rs

@@ -1,4 +1,4 @@
-use crate::{ron, DynamicSceneBuilder, Scene, SceneSpawnError};
+use crate::{DynamicSceneBuilder, Scene, SceneSpawnError};
 use bevy_asset::Asset;
 use bevy_ecs::reflect::{ReflectMapEntities, ReflectResource};
 use bevy_ecs::{
@@ -6,15 +6,18 @@ use bevy_ecs::{
     reflect::{AppTypeRegistry, ReflectComponent},
     world::World,
 };
-use bevy_reflect::{PartialReflect, TypePath, TypeRegistry};
+use bevy_reflect::{PartialReflect, TypePath};
 
 use crate::reflect_utils::clone_reflect_value;
-#[cfg(feature = "serialize")]
-use crate::serde::SceneSerializer;
 use bevy_ecs::component::ComponentCloneBehavior;
 use bevy_ecs::relationship::RelationshipHookMode;
+
 #[cfg(feature = "serialize")]
-use serde::Serialize;
+use {
+    crate::{ron, serde::SceneSerializer},
+    bevy_reflect::TypeRegistry,
+    serde::Serialize,
+};
 
 /// A collection of serializable resources and dynamic entities.
 ///

crates/bevy_scene/src/lib.rs

@@ -27,7 +27,6 @@ pub mod serde;
 /// Rusty Object Notation, a crate used to serialize and deserialize bevy scenes.
 pub use bevy_asset::ron;
 
-use bevy_ecs::schedule::IntoScheduleConfigs;
 pub use components::*;
 pub use dynamic_scene::*;
 pub use dynamic_scene_builder::*;
@@ -48,7 +47,9 @@ pub mod prelude {
 }
 
 use bevy_app::prelude::*;
-use bevy_asset::AssetApp;
+
+#[cfg(feature = "serialize")]
+use {bevy_asset::AssetApp, bevy_ecs::schedule::IntoScheduleConfigs};
 
 /// Plugin that provides scene functionality to an [`App`].
 #[derive(Default)]

crates/bevy_scene/src/scene_loader.rs

@@ -1,21 +1,27 @@
-#[cfg(feature = "serialize")]
-use crate::serde::SceneDeserializer;
-use crate::{ron, DynamicScene};
-use bevy_asset::{io::Reader, AssetLoader, LoadContext};
+use crate::ron;
 use bevy_ecs::{
     reflect::AppTypeRegistry,
     world::{FromWorld, World},
 };
 use bevy_reflect::TypeRegistryArc;
-#[cfg(feature = "serialize")]
-use serde::de::DeserializeSeed;
 use thiserror::Error;
 
+#[cfg(feature = "serialize")]
+use {
+    crate::{serde::SceneDeserializer, DynamicScene},
+    bevy_asset::{io::Reader, AssetLoader, LoadContext},
+    serde::de::DeserializeSeed,
+};
+
 /// Asset loader for a Bevy dynamic scene (`.scn` / `.scn.ron`).
 ///
 /// The loader handles assets serialized with [`DynamicScene::serialize`].
 #[derive(Debug)]
 pub struct SceneLoader {
+    #[cfg_attr(
+        not(feature = "serialize"),
+        expect(dead_code, reason = "only used with `serialize` feature")
+    )]
     type_registry: TypeRegistryArc,
 }