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/ports/framebuffer/src/lib.rs

@@ -10,4 +10,18 @@ pub trait Framebuffer {
     fn fill_rect(&mut self, x: ScreenCoord, y: ScreenCoord, w: Dimension, h: Dimension, color: Color);
     fn clear(&mut self, color: Color);
     fn flush(&mut self);
+
+    /// A run of pixels from (x, y) rightwards, clipped at the screen edge.
+    fn write_row(&mut self, x: ScreenCoord, y: ScreenCoord, pixels: &[Color]) {
+        for (i, c) in pixels.iter().enumerate() {
+            let Some(px) = u16::try_from(i).ok().and_then(|i| x.raw().checked_add(i)) else {
+                return;
+            };
+            self.write_pixel(ScreenCoord::new(px), y, *c);
+        }
+    }
+
+    /// Moves the band of rows from `top`, `height` tall, up by `by` rows,
+    /// and fills the `by` rows left at its bottom with `fill`.
+    fn scroll_up(&mut self, top: ScreenCoord, height: Dimension, by: Dimension, fill: Color);
 }