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/services/audioService.test.ts

@@ -104,7 +104,7 @@ describe('useAudioService', () => {
       const mockTrack2 = { stop: vi.fn() }
       const mockStream = {
         getTracks: vi.fn().mockReturnValue([mockTrack1, mockTrack2])
-      } as unknown as MediaStream
+      } as Partial<MediaStream> as MediaStream
 
       service.stopAllTracks(mockStream)
 
@@ -120,7 +120,7 @@ describe('useAudioService', () => {
     it('should handle stream with no tracks', () => {
       const mockStream = {
         getTracks: vi.fn().mockReturnValue([])
-      } as unknown as MediaStream
+      } as Partial<MediaStream> as MediaStream
 
       expect(() => service.stopAllTracks(mockStream)).not.toThrow()
       expect(mockStream.getTracks).toHaveBeenCalledTimes(1)
@@ -135,7 +135,7 @@ describe('useAudioService', () => {
       }
       const mockStream = {
         getTracks: vi.fn().mockReturnValue([mockTrack1, mockTrack2])
-      } as unknown as MediaStream
+      } as Partial<MediaStream> as MediaStream
 
       expect(() => service.stopAllTracks(mockStream)).toThrow()
       expect(mockTrack1.stop).toHaveBeenCalledTimes(1)

src/services/colorPaletteService.ts

@@ -107,8 +107,7 @@ export const useColorPaletteService = () => {
     for (const dataType of nodeDefStore.nodeDataTypes) {
       const cssVar = `color-datatype-${dataType}`
 
-      const valueMaybe =
-        linkColorPalette[dataType as unknown as keyof Colors['node_slot']]
+      const valueMaybe = linkColorPalette[dataType as keyof Colors['node_slot']]
       if (valueMaybe) {
         rootStyle.setProperty(`--${cssVar}`, valueMaybe)
       } else {