Function convert_optimised 

pub fn convert_optimised(
    model: &mut Model,
    bla_x: &[f32],
    on_step: &mut dyn FnMut(usize, usize) -> bool,
) -> Converted

Measure::Optimised with progress: on_step(done, total) after each optimiser step (the clean measurement and the model render before the first take about a fifth of the time). Returning false stops early with the best result so far.