fix: address PR review feedback for upstream value composable (#9908)

## Summary
follow up https://github.com/Comfy-Org/ComfyUI_frontend/pull/9851
fix https://github.com/Comfy-Org/ComfyUI_frontend/issues/9877 and
https://github.com/Comfy-Org/ComfyUI_frontend/issues/9878

- Make useUpstreamValue generic to eliminate as Bounds/CurvePoint[]
casts
- Change isBoundsObject to type predicate (value is Bounds)
- Reuse WidgetState from widgetValueStore instead of duplicate interface
- Add length >= 2 guard in isCurvePointArray for empty arrays
- Add disabled guard in effectiveBounds setter
- Add unit tests for singleValueExtractor and boundsExtractor

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9908-fix-address-PR-review-feedback-for-upstream-value-composable-3236d73d365081f7a01dcb416732544a)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/components/curve/WidgetCurve.vue

@@ -39,7 +39,7 @@ const upstreamValue = useUpstreamValue(
 
 const effectivePoints = computed(() =>
   isDisabled.value && upstreamValue.value
-    ? (upstreamValue.value as CurvePoint[])
+    ? upstreamValue.value
     : modelValue.value
 )
 </script>

src/components/curve/curveUtils.ts

@@ -3,6 +3,7 @@ import type { CurvePoint } from './types'
 export function isCurvePointArray(value: unknown): value is CurvePoint[] {
   return (
     Array.isArray(value) &&
+    value.length >= 2 &&
     value.every(
       (p) =>
         Array.isArray(p) &&

src/components/imagecrop/WidgetImageCrop.vue

@@ -148,10 +148,10 @@ const upstreamValue = useUpstreamValue(
 const effectiveBounds = computed({
   get: () =>
     isDisabled.value && upstreamValue.value
-      ? (upstreamValue.value as Bounds)
+      ? upstreamValue.value
       : modelValue.value,
   set: (v) => {
-    modelValue.value = v
+    if (!isDisabled.value) modelValue.value = v
   }
 })