perf: fast display (row runs, bulk fills, pixel scroll), terminal draws changed cells only + scrolls pixels, print! batched (was IPC per fmt fragment), snake sleeps on timer

crates/types/src/display.rs

@@ -52,6 +52,9 @@ impl Dimension {
 /// `DrawText`, shared by the display server and `libkos::display`: up to
 /// `TEXT_BYTES` characters at a pixel position, each cell `fg` on `bg`.
 /// Words: `[TEXT | len << 8 | fg << 16, x | y << 16 | bg << 32, bytes 0..8, 8..16]`.
+/// Request tag: move a band of rows up (the display server's `Scroll`).
+pub const SCROLL: usize = 7;
+
 pub mod text {
     use super::{Color, ScreenCoord};