Function merge_lo

publication/code/chapter07/tim_sort.rs:180–185

合并 A，B 为一个 run

(list: &mut [i32], first_len: usize)

// 合并 A，B 为一个 run
fn merge_lo(list: &mut [i32], first_len: usize) {
    unsafe {
        let mut state = MergeLo::new(list, first_len);
        state.merge();
    }
}

// merge_lo 排序状态体
struct MergeLo<'a> {