merge undo/redo logic for areas and single tiles

src/marble_engine/board.rs

@@ -61,6 +61,14 @@ impl Board {
 		}
 	}
 
+	pub fn new_single(tile: Tile) -> Self {
+		Self {
+			rows: vec![vec![tile]],
+			width: 1,
+			height: 1,
+		}
+	}
+
 	pub fn new(rows: Vec<Vec<Tile>>) -> Self {
 		Self {
 			width: rows[0].len(),