`.providerMetadata.openai.logprobs` is set to array of empty arrays

### Description

Reported by @shaper 

> I've started seeing in provider metadata when dumped a variably sized empty array of empty arrays for logprobs

I was able to reproduce the problem with this example provided by @shaper. I'm looking into it

```ts
import { generateText, streamText } from 'ai';
import 'dotenv/config';
import { openai, type OpenAIResponsesProviderOptions } from '@ai-sdk/openai';

async function main() {
  const options = {
    model: openai('gpt-4o-mini'),
    prompt: 'What is specifically notable about the style of Sonoran food?',
    providerOptions: {
      openai: {
      } satisfies OpenAIResponsesProviderOptions,
    },
  }
  const streamResult = await streamText(options);

  console.log(
    'PROVIDER METADATA FORM STREAMTEXT:',
    JSON.stringify(await streamResult.providerMetadata, null, 2),
  );

  const generateResult = await generateText(options);

  console.log(
    '\nPROVIDER METADATA FORM GENERATETEXT:',
    JSON.stringify(await generateResult.providerMetadata, null, 2),
  );
}

main().catch(console.error);
```

Actual Result

```
PROVIDER METADATA FORM STREAMTEXT: {
  "openai": {
    "responseId": "resp_68aa13c566ac8195a5ce4923b592b6100172e408f9c981ad",
    "logprobs": [
      [],
      [],
      [],
      [],
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      []
    ]
  }
}

PROVIDER METADATA FORM GENERATETEXT: {
  "openai": {
    "responseId": "resp_68aa13cb786481969fbbc2e08cd172ae0bda5868303ea100"
  }
}
```

Expected result

```
PROVIDER METADATA FORM STREAMTEXT: {
  "openai": {
    "responseId": "resp_68aa13c566ac8195a5ce4923b592b6100172e408f9c981ad",
  }
}

PROVIDER METADATA FORM GENERATETEXT: {
  "openai": {
    "responseId": "resp_68aa13cb786481969fbbc2e08cd172ae0bda5868303ea100"
  }
}
```

This might potentially be related to #7951

### AI SDK Version

ai: 5

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Labels: bug, ai/provider, provider/openai
State: closed