Usage
constructor(inputTokens: Usage.InputTokenBreakdown = InputTokenBreakdown(), outputTokens: Usage.OutputTokenBreakdown = OutputTokenBreakdown(), raw: JsonElement? = null)
Legacy flat (promptTokens, completionTokens) constructor — unambiguous because BOTH params are required. The primary constructor's Usage() no-arg path goes through default InputTokenBreakdown() / OutputTokenBreakdown().