* fix ToolChoiche typo
* add tool_call_id to ChatCompletionMessage
* add /chat system_fingerprint response field
* check empty ToolCallID JSON marshaling
and add omitempty for tool_call_id
* messages also required; don't omitempty
* add Type to ToolCall, required by the API
* fix test, omitempty for response_format ptr
* fix casing of role values in comments
