add a map_vector method to iterate 2 vectors at once

[xMAC94x]

if res.correction.x != 0.0 {
                        entity.vel_mut().x = 0.0;
                    }
                    if res.correction.y != 0.0 {
                        entity.vel_mut().y = 0.0;
                    }
                    if res.correction.z != 0.0 {
                        entity.vel_mut().z = 0.0;
                    }

if velocity.x.abs() / half_chunk_scale.x > speed_step_cnt {
            speed_step_cnt = velocity.x.abs() / half_chunk_scale.x;
        }
        if velocity.y.abs() / half_chunk_scale.y > speed_step_cnt {
            speed_step_cnt = velocity.y.abs() / half_chunk_scale.y;
        }
        if velocity.z.abs() / half_chunk_scale.z > speed_step_cnt {
            speed_step_cnt = velocity.z.abs() / half_chunk_scale.z;
        }