NodeMaterialObserver: Reuse lightsData cache entry per frame.

`getLights` allocated a fresh `{ renderId, lightsData }` object every
time `renderId` changed (i.e. once per frame per lightsNode). Mutate
the cached entry's fields in place instead, so the cache-miss path
doesn't allocate after the first frame.

`getLightsData` also allocated a fresh `const lights = []` per call;
change the signature to accept the output array so it can be reused.

Measured on webgpu_backdrop_water (Inspector stripped, 1 KB sampling):
site no longer appears in the top 30 allocators.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: RenaudRohlinger

src/materials/nodes/manager/NodeMaterialObserver.js

@@ -216,7 +216,7 @@ class NodeMaterialObserver {
 
 			}
 
-			data.lights = this.getLightsData( renderObject.lightsNode.getLights() );
+			data.lights = this.getLightsData( renderObject.lightsNode.getLights(), [] );
 
 			this.renderObjects.set( renderObject, data );
 
@@ -629,9 +629,9 @@ class NodeMaterialObserver {
 	 * @param {Array<Light>} materialLights - The material lights.
 	 * @return {Array<Object>} The lights data for the given material lights.
 	 */
-	getLightsData( materialLights ) {
+	getLightsData( materialLights, lights ) {
 
-		const lights = [];
+		lights.length = 0;
 
 		for ( const light of materialLights ) {
 
@@ -658,23 +658,25 @@ class NodeMaterialObserver {
 	 */
 	getLights( lightsNode, renderId ) {
 
-		if ( _lightsCache.has( lightsNode ) ) {
+		let cached = _lightsCache.get( lightsNode );
 
-			const cached = _lightsCache.get( lightsNode );
+		if ( cached !== undefined && cached.renderId === renderId ) {
 
-			if ( cached.renderId === renderId ) {
+			return cached.lightsData;
 
-				return cached.lightsData;
+		}
 
-			}
+		if ( cached === undefined ) {
 
-		}
+			cached = { renderId: - 1, lightsData: [] };
+			_lightsCache.set( lightsNode, cached );
 
-		const lightsData = this.getLightsData( lightsNode.getLights() );
+		}
 
-		_lightsCache.set( lightsNode, { renderId, lightsData } );
+		cached.renderId = renderId;
+		this.getLightsData( lightsNode.getLights(), cached.lightsData );
 
-		return lightsData;
+		return cached.lightsData;
 
 	}