fix: siliconflow error response

[sternelee]

silliconflow API error response only received message text, not a object

[VisargD]

Hey! Will it be possible to add the documentation link in the PR description to point out why this is required? It will make it easy to track things in future. Thanks!

[narengogi]

would recommend changing the structure of this function to

if ('contents' in response) {
 return response
 }
 if (responseStatus !== 200 && typeof response === 'string') {
    return SiliconFlowErrorResponseTransform(
      { message: response, code: String(responseStatus) },
      SILICONFLOW
    );
  }
  else return generateInvalidProviderResponseError(response, SILICONFLOW)

[narengogi]

Same comment for other updated functions as well