Function classify_mistral_error 

pub fn classify_mistral_error(
    status: u16,
    message: impl Into<String>,
    retry_after: Option<f64>,
) -> Error

Classify a non-success Mistral Chat Completions API HTTP response into a granular Error.

Mistral’s documented error body is {"object":"error","message":..., "type":...,"param":...,"code":...} (OpenAI-shaped but without a nested error wrapper). This maps by HTTP status only:

• 401 / 403 -> Error::ServiceInvalidAuth
• 400 / 422 -> Error::ServiceInvalidRequest
• anything else — notably 408 / 429 / 5xx, which the retry layer depends on — -> Error::ServiceStatus, unchanged

Unlike OpenAI, Mistral has no documented content-filter-specific error marker to key off of (no code: "content_filter" convention), so this never constructs Error::ServiceContentFilter – don’t invent one.