Constant glassbench::OPTIMAL_DURATION_NS

pub const OPTIMAL_DURATION_NS: u128 = Duration::from_secs(2).as_nanos(); // 0_x00_000_000_000_000_000_000_000_077_359_400u128

How long we’d like the measures of a task to go. Will be divided by the duration of a task in the estimate phase to decide how many iterations we’ll do for measures