Structured error returned from WhisperCpp calls.
reason is one of:
:invalid_request- bad arguments (bad path, malformed audio).:load_error- whisper.cpp could not load the GGML/GGUF model file.:inference_error- the Whisper model returned an error during decoding.:runtime_error- internal NIF runtime fault (e.g. poisoned mutex).:nif_panic- the Rust side panicked; should never happen in practice.:native_error- fallback for unrecognised native error types.