Implemented Entity tagged union for highlighted entity (similar to abstract class in some ways)

src/common/constants.zig

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+const clr = @import("raylib").Color;
+
+/// Screen Width
+pub const WIDTH = 1366;
+/// Screen Height
+pub const HEIGHT = 768;
+pub const BACKGROUND_COLOR = clr.light_gray;
+
+/// Base node radius
+pub const NODE_RADIUS = 20;
+/// The radius around node center where no new node gets created but rather it snaps onto existing one
+pub const NODE_SNAP_RADIUS = 3 * NODE_RADIUS;
+/// Regular (finished) node colour
+pub const NODE_COLOUR = clr.brown;
+/// Temporary node colour - currently being pulled from
+pub const NODE_TEMP_COLOUR = clr.orange;
+/// The colour of the node being at the cursor
+pub const NODE_CURSOR_COLOUR = clr.blue;
+
+/// Road (line) size
+pub const ROAD_SIZE = 20;
+/// Regular road colour
+pub const ROAD_COLOUR = clr.black;
+/// Colour of the road that is highlighted
+pub const ROAD_HIGHLIGHTED_COLOUR = clr.green;
+
+pub const TEXT_SIZE = 50;
+pub const TEXT_COLOUR = clr.black;