refactor(render): cleanup add_import_to_composer (#19269)

# Objective

- Reduce nesting

## Solution

- Refactor

## Testing

- `bevy run --example=3d_scene web --open`

crates/bevy_render/src/render_resource/pipeline_cache.rs

@@ -203,28 +203,25 @@ impl ShaderCache {
         shaders: &HashMap<AssetId<Shader>, Shader>,
         import: &ShaderImport,
     ) -> Result<(), PipelineCacheError> {
-        if !composer.contains_module(&import.module_name()) {
-            if let Some(shader_handle) = import_path_shaders.get(import) {
-                if let Some(shader) = shaders.get(shader_handle) {
-                    for import in &shader.imports {
-                        Self::add_import_to_composer(
-                            composer,
-                            import_path_shaders,
-                            shaders,
-                            import,
-                        )?;
-                    }
-
-                    composer.add_composable_module(shader.into())?;
-                } else {
-                    Err(PipelineCacheError::ShaderImportNotYetAvailable)?;
-                }
-            } else {
-                Err(PipelineCacheError::ShaderImportNotYetAvailable)?;
-            }
-            // if we fail to add a module the composer will tell us what is missing
+        // Early out if we've already imported this module
+        if composer.contains_module(&import.module_name()) {
+            return Ok(());
         }
 
+        // Check if the import is available (this handles the recursive import case)
+        let shader = import_path_shaders
+            .get(import)
+            .and_then(|handle| shaders.get(handle))
+            .ok_or(PipelineCacheError::ShaderImportNotYetAvailable)?;
+
+        // Recurse down to ensure all import dependencies are met
+        for import in &shader.imports {
+            Self::add_import_to_composer(composer, import_path_shaders, shaders, import)?;
+        }
+
+        composer.add_composable_module(shader.into())?;
+        // if we fail to add a module the composer will tell us what is missing
+
         Ok(())
     }