Accept null score in hf-inference image-segmentation response

The image-segmentation output schema declares score as optional
(packages/tasks/src/tasks/image-segmentation/inference.ts: score?: number),
but the runtime validator in HFInferenceImageSegmentationTask only
accepted undefined or a number, rejecting null with:

  API Implementation Error: TypeError: Invalid output: output must be
  of type Array<{label:string; score:number; mask: string}>

Several HF-Inference models (e.g. jonathandinu/face-parsing) return
null for score on per-segment masks, which is consistent with the
optional schema field but tripped the strict type guard.

Allow null alongside undefined and number.

Refs #1430

Author: Sanjays2402

packages/inference/src/providers/hf-inference.ts

@@ -393,7 +393,7 @@ export class HFInferenceImageSegmentationTask extends HFInferenceTask implements
 				(x) =>
 					typeof x.label === "string" &&
 					typeof x.mask === "string" &&
-					(x.score === undefined || typeof x.score === "number"),
+					(x.score === undefined || x.score === null || typeof x.score === "number"),
 			)
 		) {
 			return response;