[Inference Providers] provider="auto"

[hanouticelina]

Same as huggingface/huggingface_hub#3011.

This PR adds support for auto selection of the provider. Previously the default value was hf-inference (HF Inference API provider), now we default to "auto", meaning we will select the first of the providers available for the model, sorted by the user's order in https://hf.co/settings/inference-providers.

you can test with:

import { chatCompletion } from "../src";

const res = await chatCompletion({
	// provider="auto",
	model: "deepseek-ai/DeepSeek-V3-0324",
	messages: [
		{
			role: "user",
			content: "What is the capital of France?",
		},
	],
	accessToken: process.env.HF_TOKEN,
});
console.log(res.choices[0].message.content);

Defaulting to 'auto' which will select the first provider available for the model, sorted by the user's order in https://hf.co/settings/inference-providers.
Auto-selected provider: sambanova
The capital of France is **Paris**. It is known for its iconic landmarks such as the Eiffel Tower...blabla

the selected provider should be be the first in inferenceProviderMapping mapping here: https://huggingface.co/api/models/deepseek-ai/DeepSeek-V3-0324?expand=inferenceProviderMapping

[hanouticelina]

this could be done in getProviderHelper as we did for the python client, but that would make the function async and we would have to update the snippets generation as well

[hanouticelina]

if provider="auto", we call fetchInferenceProviderMappingForModel 2 times: once to resolve the provider and a second time in makeRequestOptions. this cache avoids the extra HTTP call.