feat(tree): add flat and lazy modes for tree data handling

* Implement flat mode to transform flat data with parentId to nested structure.
* Introduce lazy mode for on-demand loading of children.
* Update tree rendering logic to accommodate new modes.
* Enhance tree cell expansion logic to support lazy loading.
* Add dark mode styles for improved UI experience.
* Create comprehensive end-to-end tests for tree functionality.

src/Griddy/core/GriddyStore.ts

@@ -82,16 +82,16 @@ export interface GriddyStoreState extends GriddyUIState {
   setScrollRef: (el: HTMLDivElement | null) => void;
   // ─── Internal ref setters ───
   setTable: (table: Table<any>) => void;
-  setVirtualizer: (virtualizer: Virtualizer<HTMLDivElement, Element>) => void;
+  setTreeChildrenCache: (nodeId: string, children: any[]) => void;
 
+  setTreeLoadingNode: (nodeId: string, loading: boolean) => void;
+  setVirtualizer: (virtualizer: Virtualizer<HTMLDivElement, Element>) => void;
   showToolbar?: boolean;
   sorting?: SortingState;
   // ─── Tree/Hierarchical Data ───
   tree?: TreeConfig<any>;
-  treeLoadingNodes: Set<string>;
   treeChildrenCache: Map<string, any[]>;
-  setTreeLoadingNode: (nodeId: string, loading: boolean) => void;
-  setTreeChildrenCache: (nodeId: string, children: any[]) => void;
+  treeLoadingNodes: Set<string>;
   // ─── Synced from GriddyProps (written by $sync) ───
   uniqueId?: string;
 }
@@ -150,10 +150,12 @@ export const { Provider: GriddyProvider, useStore: useGriddyStore } = createSync
   setTable: (table) => set({ _table: table }),
 
   setTotalRows: (count) => set({ totalRows: count }),
-  setVirtualizer: (virtualizer) => set({ _virtualizer: virtualizer }),
-  // ─── Tree State ───
-  treeLoadingNodes: new Set(),
-  treeChildrenCache: new Map(),
+  setTreeChildrenCache: (nodeId, children) =>
+    set((state) => {
+      const newMap = new Map(state.treeChildrenCache);
+      newMap.set(nodeId, children);
+      return { treeChildrenCache: newMap };
+    }),
   setTreeLoadingNode: (nodeId, loading) =>
     set((state) => {
       const newSet = new Set(state.treeLoadingNodes);
@@ -164,12 +166,10 @@ export const { Provider: GriddyProvider, useStore: useGriddyStore } = createSync
       }
       return { treeLoadingNodes: newSet };
     }),
-  setTreeChildrenCache: (nodeId, children) =>
-    set((state) => {
-      const newMap = new Map(state.treeChildrenCache);
-      newMap.set(nodeId, children);
-      return { treeChildrenCache: newMap };
-    }),
+  setVirtualizer: (virtualizer) => set({ _virtualizer: virtualizer }),
   // ─── Row Count ───
   totalRows: 0,
+  treeChildrenCache: new Map(),
+  // ─── Tree State ───
+  treeLoadingNodes: new Set(),
 }));