feat: enhance layer mask handling and opacity management

- Introduced `getLayerMask` utility to streamline layer mask retrieval.
- Updated layer rendering logic to incorporate layer masks and opacity adjustments.
- Added functionality to prevent dropping a group into its descendants.
- Enhanced image texture rendering to support opacity parameters across various rendering functions.
- Implemented group layer bounds application for better scaling and positioning.
- Added tests to ensure correct behavior when handling layer masks and group layers.
- Created new types for asset generation provenance to track generated assets more effectively.

editor/state.ts

@@ -79,9 +79,12 @@ export type GenerationCandidate = {
   };
 };
 
+export type GenerationCompareMode = "result" | "before" | "split";
+
 export type GenerationState = {
   candidates: GenerationCandidate[];
   selectedCandidateId?: string;
+  compareMode: GenerationCompareMode;
 };
 
 export type EditorState = {