make erase a bit more efficient

src/terminal/Screen.zig

@@ -74,6 +74,11 @@ pub fn rowIterator(self: *const Screen) RowIterator {
     return .{ .screen = self, .index = 0 };
 }
 
+/// Get the visible portion of the screen.
+pub fn getVisible(self: Screen) []Cell {
+    return self.storage;
+}
+
 /// Get a single row by index (0-indexed).
 pub fn getRow(self: Screen, idx: usize) Row {
     // Get the index of the first byte of the the row at index.

src/terminal/Terminal.zig

@@ -223,15 +223,8 @@ pub fn eraseDisplay(
 ) !void {
     switch (mode) {
         .complete => {
-            var y: usize = 0;
-            while (y < self.rows) : (y += 1) {
-                var x: usize = 0;
-                while (x < self.cols) : (x += 1) {
-                    const cell = try self.getOrPutCell(alloc, x, y);
-                    cell.* = self.cursor.pen;
-                    cell.char = 0;
-                }
-            }
+            const all = self.screen.getVisible();
+            std.mem.set(Screen.Cell, all, self.cursor.pen);
         },
 
         .below => {