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/workbench/extensions/manager/utils/graphHasMissingNodes.test.ts

@@ -86,10 +86,7 @@ describe('graphHasMissingNodes', () => {
   })
 
   it('ignores nodes without a type', () => {
-    const graph = createGraph([
-      createNode(undefined),
-      createNode(null as unknown as string)
-    ])
+    const graph = createGraph([createNode(undefined), createNode(null!)])
 
     expect(graphHasMissingNodes(graph, {})).toBe(false)
   })