UsageInfo (chat completion usage) is missing prompt_tokens_details #240

Hey there

Mistral is now supporting prompt caching, however, there is 0 support for this with this SDK.

Per the prompt caching docs, completion responses report cached tokens at usage.prompt_tokens_details.cached_tokens:

"usage": {
  "prompt_tokens": 1013,
  "total_tokens": 1043,
  "completion_tokens": 30,
  "prompt_tokens_details": { "cached_tokens": 1008 }
}

However, ChatCompletionResponse is typed as UsageInfo, and UsageInfo does not declare prompt_tokens_details.

Seems you rely on Speakeasy and codegen to build this SDK so it should be a quick win ;)