Function aria_complete_stream 

#[unsafe(no_mangle)]
pub extern "C" fn aria_complete_stream(
    model: *mut AriaModel,
    messages_json: *const i8,
    options_json: *const i8,
    tools_json: *const i8,
    out: *mut i8,
    out_len: usize,
    callback: Option<unsafe extern "C" fn(*const i8, *mut c_void)>,
    user_data: *mut c_void,
) -> i32

Streaming chat; callback receives each chunk as a C string.