Parallel iteration

[rickwebiii]

Parallel BSK generation

[samtay]

Lgtm. Just want to call out that you have now changed all the dst_iters to have parallel capabilities, which is probably fine, but if this is only relevant for a few cases, you could define a different variant of the dst_iter! macro too. E.g.

macro_rules! dst_iter {
    ($t:ty, $t_mut:ty, $wrapper_type: ty, $item_ref:ty, ($($t_bounds:ty,)*)) => {
        // existing stuff
    }
    ($t:ty, $t_mut:ty, $par_t:ty, $par_t_mut:ty, $wrapper_type: ty, $item_ref:ty, ($($t_bounds:ty,)*)) => {
        dst_iter! { $t, $t_mut, $wrapper_type, $item_ref, ($($t_bounds,)*) }
        // new parallel stuff
    }