use static, fixed arrays for circle geometry data instead of allocating for each one

include/twn_draw.h

@@ -22,6 +22,7 @@ TWN_API void draw_sprite(char const *path,
 TWN_API void draw_rectangle(Rect rect, Color color);
 
 /* pushes a filled circle onto the circle render queue */
+/* note that its edges may look jagged with a radius larger than 2048 */
 TWN_API void draw_circle(Vec2 position, float radius, Color color);
 
 /* TODO: have font optional, with something minimal coming embedded */