fix: replace as-unknown-as casts with safer patterns (#9107)

## Summary

- Replace 83 `as unknown as` double casts with safer alternatives across
33 files
- Use `as Partial<X> as X` pattern where TypeScript allows it
- Create/reuse factory functions from `litegraphTestUtils.ts` for mock
objects
- Widen `getWorkflowDataFromFile` return type to include `ComfyMetadata`
directly
- Reduce total `as unknown as` count from ~153 to 71

The remaining 71 occurrences are genuinely necessary due to cross-schema
casts, generic variance, missing index signatures, Float64Array-to-tuple
conversions, and DOM type incompatibilities.

## Test plan

- [x] `pnpm typecheck` passes
- [x] `pnpm lint` passes
- [x] All affected unit tests pass

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9107-fix-replace-as-unknown-as-casts-with-safer-patterns-3106d73d3650815cb5bcd613ad635bd7)
by [Unito](https://www.unito.io)

src/composables/node/useNodePreviewAndDrag.test.ts

@@ -72,7 +72,9 @@ describe('useNodePreviewAndDrag', () => {
         toJSON: () => ({})
       })
 
-      const mockEvent = { currentTarget: mockElement } as unknown as MouseEvent
+      const mockEvent = {
+        currentTarget: mockElement
+      } as Partial<MouseEvent> as MouseEvent
       result.handleMouseEnter(mockEvent)
 
       expect(result.isHovered.value).toBe(true)
@@ -83,7 +85,9 @@ describe('useNodePreviewAndDrag', () => {
       const result = useNodePreviewAndDrag(nodeDef)
 
       const mockElement = document.createElement('div')
-      const mockEvent = { currentTarget: mockElement } as unknown as MouseEvent
+      const mockEvent = {
+        currentTarget: mockElement
+      } as Partial<MouseEvent> as MouseEvent
       result.handleMouseEnter(mockEvent)
 
       expect(result.isHovered.value).toBe(false)
@@ -150,7 +154,7 @@ describe('useNodePreviewAndDrag', () => {
       const mockEvent = {
         clientX: 100,
         clientY: 200
-      } as unknown as DragEvent
+      } as Partial<DragEvent> as DragEvent
 
       result.handleDragEnd(mockEvent)
 
@@ -168,7 +172,7 @@ describe('useNodePreviewAndDrag', () => {
         dataTransfer: { dropEffect: 'none' },
         clientX: 300,
         clientY: 400
-      } as unknown as DragEvent
+      } as Partial<DragEvent> as DragEvent
 
       result.handleDragEnd(mockEvent)