[Inference Providers] Fix fal image-to-image API payload (#1858)

this should fix inference for
https://huggingface.co/black-forest-labs/FLUX.2-dev

it seems like some fal `image-to-image` endpoints expect `image_urls` as
an array, not `image_url` as a string (see the specs for Flux.2
[here](https://fal.ai/models/fal-ai/flux-2/lora/edit/api#schema-input)).
Note that other models like
[Qwen-Image-Edit](https://huggingface.co/Qwen/Qwen-Image-Edit?inference_provider=fal-ai)
still expects `image_url` as input (specs
[here](https://fal.ai/models/fal-ai/qwen-image-edit/api#schema-input)).

Author: hanouticelina

packages/inference/src/providers/fal-ai.ts

@@ -240,13 +240,16 @@ export class FalAIImageToImageTask extends FalAiQueueTask implements ImageToImag
 
 	async preparePayloadAsync(args: ImageToImageArgs): Promise<RequestArgs> {
 		const mimeType = args.inputs instanceof Blob ? args.inputs.type : "image/png";
+		const imageDataUrl = `data:${mimeType};base64,${base64FromBytes(
+			new Uint8Array(args.inputs instanceof ArrayBuffer ? args.inputs : await (args.inputs as Blob).arrayBuffer())
+		)}`;
 		return {
 			...omit(args, ["inputs", "parameters"]),
-			image_url: `data:${mimeType};base64,${base64FromBytes(
-				new Uint8Array(args.inputs instanceof ArrayBuffer ? args.inputs : await (args.inputs as Blob).arrayBuffer())
-			)}`,
+			image_url: imageDataUrl,
 			...args.parameters,
 			...args,
+			// Some fal endpoints (e.g. FLUX.2-dev) expect `image_urls` (array) instead of `image_url`
+			image_urls: [imageDataUrl],
 		};
 	}